Stockholders' Equity - Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance			$ 1,156
Other comprehensive income (loss), net of tax	$ 302	$ 830	2,833	$ 1,433
AOCI ending balance	3,981		3,981
Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	2,151	(147)	935	(439)
Other comprehensive income (loss) before reclassifications	222	284	1,446	594
Amounts reclassified from AOCI into earnings	0	(12)	0	(30)
Other comprehensive income (loss), net of tax	222	272	1,446	564
AOCI ending balance	2,373	125	2,373	125
Accumulated Net Unrealized Investment Gain (Loss) | Securities Held to Maturity
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance		(184)		(190)
Other comprehensive income (loss) before reclassifications		0		0
Amounts reclassified from AOCI into earnings		6		12
Other comprehensive income (loss), net of tax		6		12
AOCI ending balance		(178)		(178)
Hedging Relationships
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	1,728	(141)	354	(418)
Other comprehensive income (loss) before reclassifications	(60)	406	1,635	517
Amounts reclassified from AOCI into earnings	117	131	(204)	297
Other comprehensive income (loss), net of tax	57	537	1,431	814
AOCI ending balance	1,785	396	1,785	396
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(174)	(147)	(107)	(177)
Other comprehensive income (loss) before reclassifications	23	15	(44)	45
Amounts reclassified from AOCI into earnings	0	0	0	0
Other comprehensive income (loss), net of tax	23	15	(44)	45
AOCI ending balance	(151)	(132)	(151)	(132)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(26)	(41)	(26)	(39)
Other comprehensive income (loss) before reclassifications	0	0	0	(1)
Amounts reclassified from AOCI into earnings	0	0	0	(1)
Other comprehensive income (loss), net of tax	0	0	0	(2)
AOCI ending balance	(26)	(41)	(26)	(41)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	3,679	(660)	1,156	(1,263)
Other comprehensive income (loss) before reclassifications	185	705	3,037	1,155
Amounts reclassified from AOCI into earnings	117	125	(204)	278
Other comprehensive income (loss), net of tax	302	830	2,833	1,433
AOCI ending balance	3,981	170	3,981	170
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Gains (losses) recorded in AOCI	$ (8)	$ 53	134	$ 19
Cumulative effects from adoption of the CECL standard | Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance			(8)
Cumulative effects from adoption of the CECL standard | Hedging Relationships
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance			0
Cumulative effects from adoption of the CECL standard | Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance			0
Cumulative effects from adoption of the CECL standard | Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance			0
Cumulative effects from adoption of the CECL standard | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance			$ (8)