Annual report pursuant to Section 13 and 15(d)


In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
May 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Number of stock-based awards authorized to be granted to executives, employees and non-employee directors under the 2012 Omnibus Plant (in shares)       3,500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Stock options' expiration from the date of grant 10 years      
Stock options vesting period 3 years 2 years    
Stock options granted for every even block of 100 KESIP shares purchased by the employee 50cmi_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsForBlocksOfKESIPShares      
Number of shares in every even block of KESIP shares 100us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction      
Compensation expense (net of estimated forfeitures) $ 35us-gaap_AllocatedShareBasedCompensationExpense $ 34us-gaap_AllocatedShareBasedCompensationExpense $ 35us-gaap_AllocatedShareBasedCompensationExpense  
Excess tax benefit / (deficiency) associated with share-based plans 5us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 13us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 14us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense  
Total unrecognized compensation expense (net of estimated forfeitures) $ 32us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized      
Weighted-average maximum period of recognition of total unrecognized compensation expense related to nonvested awards 2 years      
Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award        
Performance period 3 years      
Performance Shares | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award        
Target award based on the actual ROE performance (as a percent) 0.00%cmi_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfTargetAwardBasedOnActualROEPerformanceDuringTwoYearPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Performance Shares | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award        
Target award based on the actual ROE performance (as a percent) 200.00%cmi_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfTargetAwardBasedOnActualROEPerformanceDuringTwoYearPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Restricted Shares        
Share-based Compensation Arrangement by Share-based Payment Award        
Restricted shares released after two years (as a percent) 33.33%cmi_ShareBasedCompensationArrangementByShareBasedPaymentAwardPortionOfSharesReleasedAfterTwoYears
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Period after which portion of issued restricted shares will be released 2 years      
Restricted shares released on the grant date each year after the first two years (as a percent) 33.33%cmi_ShareBasedCompensationArrangementByShareBasedPaymentAwardPortionOfSharesReleasedEachYear
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Restriction period to recognize compensation expense 4 years