Fair Value Measurements - Included in Earnings (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Gains (losses) on derivative and hedging activities, net	$ 12	$ (308)	$ (29)	$ (253)
Gain (Losses) on Derivative Instruments [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Gains (losses) on derivative and hedging activities, net	2	(277)	6	(195)
Interest Expense [Member]
Fair Value Net Derivative Asset Liability Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Gains (losses) on derivative and hedging activities, net	$ 10	$ (31)	$ (35)	$ (58)