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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivatives	$ 0	$ (2)	$ 113	$ 6
Net Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified From AOCI into Income	(4)	(9)	(10)	(19)
Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivatives	0	0	0	1
Foreign exchange contracts [Member] | Net Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified From AOCI into Income	0	0	0	0
Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivatives	0	(2)	113	5
Interest rate contracts [Member] | Net Interest Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassified From AOCI into Income	$ (4)	$ (9)	$ (10)	$ (19)