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Components of Net Postemployment Costs (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]      
Service cost $ 5 $ 7 $ 7
Interest cost 4 6 5
Amortization of net gains (3) (1) 0
Net periodic benefit cost $ 6 $ 12 $ 12