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Derivative Financial Instruments - Effect of Derivative Instruments on Consolidated Statements of Income (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of gain (loss) recognized in income on derivative (ineffective portion) $ 0 $ 15  
Amount of Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing) $ (1) $ 8  
Scenario, Forecast [Member]      
Derivative Instruments, Gain (Loss) [Line Items]      
Accumulated other comprehensive income (loss), reclassified     $ 17