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Changes in Accumulated Postemployment Benefit Obligations (Detail) - Postemployment Benefit Plans - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]      
Accrued benefit obligation at January 1 $ 71 $ 95  
Service cost 5 7 $ 7
Interest cost 4 6 5
Benefits paid (6) (9)  
Assumption changes 0 (21)  
Actuarial losses/(gains) 2 (7)  
Accrued benefit obligation at December 31 $ 76 $ 71 $ 95