| 
           SHAREHOLDERS' EQUITY (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified 
         | 
        12 Months Ended | 
        1 Months Ended | 
        3 Months Ended | 
        1 Months Ended | 
      
      
        | 
           Dec. 31, 2014 
         | 
        
           Dec. 31, 2013 
         | 
        
           Dec. 31, 2012 
         | 
        
           Jul. 31, 2013 
         | 
        
           Jul. 31, 2012 
         | 
        
           Jul. 31, 2011 
         | 
        
           Dec. 31, 2014 
         | 
        
           Sep. 28, 2014 
         | 
        
           Jun. 29, 2014 
         | 
        
           Mar. 30, 2014 
         | 
        
           Dec. 31, 2013 
         | 
        
           Sep. 29, 2013 
         | 
        
           Jun. 30, 2013 
         | 
        
           Mar. 31, 2013 
         | 
        
           Dec. 31, 2012 
         | 
        
           Sep. 30, 2012 
         | 
        
           Jul. 01, 2012 
         | 
        
           Apr. 01, 2012 
         | 
        
           Jul. 31, 2014 
         | 
        
           Dec. 31, 2012 
         | 
      
      
        | Changes in shares of stock | 
         
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        | Shares acquired (in shares) | 
        
4.8us-gaap_TreasuryStockSharesAcquired
 | 
         
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        | Dividends Paid | 
         
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        | Dividend payments on common stock (in dollars) | 
        
$ 512,000,000us-gaap_PaymentsOfDividends
 | 
        
$ 420,000,000us-gaap_PaymentsOfDividends
 | 
        
$ 340,000,000us-gaap_PaymentsOfDividends
 | 
         
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        | Employee Benefits Trust | 
         
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        | Contributions charged to income (in dollars) | 
        
35,000,000us-gaap_AllocatedShareBasedCompensationExpense
 | 
        
34,000,000us-gaap_AllocatedShareBasedCompensationExpense
 | 
        
35,000,000us-gaap_AllocatedShareBasedCompensationExpense
 | 
         
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        | Preferred Stock | 
         
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        | Class of Stock | 
         
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        | Preferred Stock, Shares Authorized | 
        
1us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_PreferredStockMember
 | 
         
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1us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = us-gaap_PreferredStockMember
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        | Preference Stock | 
         
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        | Class of Stock | 
         
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        | Preferred Stock, Shares Authorized | 
        
1us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = cmi_PreferenceStockMember
 | 
         
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1us-gaap_PreferredStockSharesAuthorized / us-gaap_StatementClassOfStockAxis = cmi_PreferenceStockMember
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        | Common Stock | 
         
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        | Changes in shares of stock | 
         
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        | Balance at beginning of period (in shares) | 
        
222.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
222.4us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
222.2us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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222.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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222.4us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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222.2us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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        | Stock Issued During Period, Shares, New Issues | 
        
0.1us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
0.1us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
0.4us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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        | Other shareholder transactions (in shares) | 
        
(0.1)cmi_OtherShareholderTransactions / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
(0.2)cmi_OtherShareholderTransactions / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
(0.2)cmi_OtherShareholderTransactions / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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        | Balance at the end of the period (in shares) | 
        
222.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
222.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
222.4us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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222.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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222.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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222.4us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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222.4us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
      
      
        | Dividends Paid | 
         
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        | Cash dividend (in dollars per share) | 
        
$ 2.81us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 2.25us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 1.8us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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$ 0.78us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.78us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.625us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.625us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.625us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.625us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.50us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.50us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.50us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.50us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.40us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
$ 0.40us-gaap_CommonStockDividendsPerShareCashPaid / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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        | Employee Benefits Trust | 
         
 | 
         
 | 
         
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        | Percentage increase in cash dividend per common share | 
         
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25.00%cmi_PercentageIncreaseDecrease / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
25.00%cmi_PercentageIncreaseDecrease / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
        
25.00%cmi_PercentageIncreaseDecrease / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember
 | 
         
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 | 
      
      
        | Treasury Stock | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
         
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 | 
      
      
        | Changes in shares of stock | 
         
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        | Balance at beginning of period (in shares) | 
        
35.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
32.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
30.2us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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35.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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32.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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30.2us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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        | Shares acquired (in shares) | 
        
4.8us-gaap_TreasuryStockSharesAcquired / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
3.3us-gaap_TreasuryStockSharesAcquired / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
2.6us-gaap_TreasuryStockSharesAcquired / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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        | Stock Issued During Period, Shares, New Issues | 
        
(0.3)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
(0.3)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
(0.2)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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        | Balance at the end of the period (in shares) | 
        
40.1us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
35.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
32.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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40.1us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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35.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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32.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
         
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32.6us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
      
      
        | Treasury Stock | 
         
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        | Treasury Stock Repurchase Authorization Value | 
         
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1,000,000,000cmi_TreasuryStockRepurchaseAuthorizationValue / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
        
1,000,000,000cmi_TreasuryStockRepurchaseAuthorizationValue / us-gaap_StatementClassOfStockAxis = us-gaap_TreasuryStockMember
 | 
      
      
        | Common Stock Held in Trust | 
         
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 | 
      
      
        | Changes in shares of stock | 
         
 | 
         
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        | Balance at beginning of period (in shares) | 
        
1.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
1.5us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
1.8us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
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1.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
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 | 
        
1.5us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
 | 
         
 | 
        
1.8us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
 | 
      
      
        | Stock Issued During Period, Shares, New Issues | 
        
(0.2)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
(0.2)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
(0.3)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
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 | 
         
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 | 
         
 | 
         
 | 
         
 | 
      
      
        | Balance at the end of the period (in shares) | 
        
1.1us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
1.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
1.5us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
 | 
         
 | 
        
1.1us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
 | 
         
 | 
        
1.3us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
 | 
         
 | 
        
1.5us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
 | 
         
 | 
         
 | 
        
1.5us-gaap_SharesIssued / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
      
      
        | Employee Benefits Trust | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
         
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 | 
         
 | 
         
 | 
         
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 | 
         
 | 
         
 | 
         
 | 
         
 | 
         
 | 
      
      
        | Contributions charged to income (in dollars) | 
        
$ 24,000,000us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
$ 24,000,000us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
        
$ 27,000,000us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_StatementClassOfStockAxis = cmi_CommonStockHeldInTrustMember
 | 
         
 | 
         
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