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Derivative Financial Instruments - Effect of Derivative Instruments on Consolidated Statements of Income (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]          
Accumulated other comprehensive income (loss), reclassified $ (7) $ (32) $ (2) $ (84)  
Amount of gain (loss) recognized in income on derivative (ineffective portion)     13 (17)  
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)     $ 5 $ 1  
Scenario, Forecast [Member]          
Derivative Instruments, Gain (Loss) [Line Items]          
Accumulated other comprehensive income (loss), reclassified         $ 8