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Income Tax - Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]      
Balance at beginning of year $ 238 $ 226 $ 313
Additions based on tax positions related to the current year 43 34 38
Additions for tax positions of prior years 13 1  
Reduction for tax positions of prior years (9) (13) (48)
Settlements (2)   (48)
Prepayment (4)   (3)
Reductions due to lapse of statute of limitations   (4) (1)
Foreign currency translation 31 (6) (25)
Balance at end of year $ 310 $ 238 $ 226