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Benefit Obligation of Postretirement Benefit Plans (Detail) - Postretirement Benefit Plans - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]      
Accrued benefit obligation at January 1 $ 511 $ 538  
Service cost 12 15 $ 13
Interest cost 20 22 22
Benefits paid (14) (10)  
Plan amendments [1] (149)    
Currency 3 (22)  
Assumption changes 34 (30)  
Actuarial (gains) / losses (23) (2)  
Accrued benefit obligation at December 31 $ 394 $ 511 $ 538
[1] Plan amendments included a change in eligibility requirements related to medical and life insurance benefits and a change in benefits for Medicare-eligible participants.