Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT BENEFITS - (Details 5 ) - Level 3 Fair Value Reconciliation

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PENSION AND OTHER POSTRETIREMENT BENEFITS - (Details 5 ) - Level 3 Fair Value Reconciliation - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
UNITED STATES      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets $ 2,937 $ 3,166  
UNITED STATES | Fair Value, Inputs, Level 3      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 316 246 $ 212
Unrealized gains (losses) on assets still held at the reporting date 39 29  
Purchases, sales and settlements, net 31 5  
UNITED STATES | Fair Value, Inputs, Level 3 | Private equity / venture capital      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 247 180 148
Unrealized gains (losses) on assets still held at the reporting date 33 24  
Purchases, sales and settlements, net 34 8  
UNITED STATES | Fair Value, Inputs, Level 3 | Real estate      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 69 66 64
Unrealized gains (losses) on assets still held at the reporting date 6 5  
Purchases, sales and settlements, net (3) (3)  
UNITED KINGDOM      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 1,782 1,960  
UNITED KINGDOM | Fair Value, Inputs, Level 3      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 686 671 613
Unrealized gains (losses) on assets still held at the reporting date (16) 76  
Purchases, sales and settlements, net 31 (18)  
UNITED KINGDOM | Fair Value, Inputs, Level 3 | Private equity / venture capital      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 187 135 117
Unrealized gains (losses) on assets still held at the reporting date 21 28  
Purchases, sales and settlements, net 31 (10)  
UNITED KINGDOM | Fair Value, Inputs, Level 3 | Real estate      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 57 59 57
Unrealized gains (losses) on assets still held at the reporting date (2) 10  
Purchases, sales and settlements, net 0 (8)  
UNITED KINGDOM | Fair Value, Inputs, Level 3 | Insurance      
Summary of changes in the fair value of level 3 assets      
Fair value of plan assets 442 477 $ 439
Unrealized gains (losses) on assets still held at the reporting date (35) 38  
Purchases, sales and settlements, net $ 0 $ 0