Derivative Financial Instruments - Gains and Losses on Derivative Instruments Designated and Qualifying As Hedging Instruments in Cash Flow Hedges (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivatives(1)	[1]	$ (2)		$ 6
Gain (Loss) Recognized in AOCI on Derivatives(1)	[1]		$ 8		$ 6
Gain (Loss) Reclassified From AOCI into Income(1)	[1]	(9)		(19)
Gain (Loss) Reclassified From AOCI into Income(1)	[1]		(5)		(9)
Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivatives(1)	[1]	0		1
Gain (Loss) Recognized in AOCI on Derivatives(1)	[1]		(1)		(6)
Foreign exchange contracts [Member] | Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified From AOCI into Income(1)	[1]	0		0
Gain (Loss) Reclassified From AOCI into Income(1)	[1]		0		0
Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivatives(1)	[1]	(2)		5
Gain (Loss) Recognized in AOCI on Derivatives(1)	[1]		9		12
Interest rate contracts [Member] | Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified From AOCI into Income(1)	[1]	$ (9)		$ (19)
Gain (Loss) Reclassified From AOCI into Income(1)	[1]		$ (5)		$ (9)

[1] As a result of adopting new accounting guidance discussed in Note 21, "New Accounting Pronouncements," beginning January 1, 2019, gains and losses on the derivatives in cash flow hedges are initially reported in AOCI and then reclassified into earnings in the same accounting period in which the designated forecasted transaction or hedged item affects earnings. Prior to January 1, 2019, cash flow hedge ineffectiveness was separately measured and reported immediately in other income (loss). Cash flow hedge ineffectiveness was immaterial during the three and six months ended June 30, 2018.