Stockholders' Equity - Change in AOCI Gain (Loss) by Component (Net of Tax) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	$ (616)	$ (430)
Other comprehensive income (loss) before reclassifications	596	234
Net realized (gains) losses reclassified from AOCI into earnings	(21)	(16)
Other comprehensive income (loss), net of tax	575	218
AOCI ending balance	(41)	(212)
Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	162	410
Other comprehensive income (loss) before reclassifications	182	114
Net realized (gains) losses reclassified from AOCI into earnings	5	8
Other comprehensive income (loss), net of tax	187	122
AOCI ending balance	349	532
Accumulated Net Unrealized Investment Gain (Loss) | Securities Held to Maturity
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(725)	(821)
Other comprehensive income (loss) before reclassifications	0	0
Net realized (gains) losses reclassified from AOCI into earnings	21	20
Other comprehensive income (loss), net of tax	21	20
AOCI ending balance	(704)	(801)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	120	10
Other comprehensive income (loss) before reclassifications	426	205
Net realized (gains) losses reclassified from AOCI into earnings	(49)	(43)
Other comprehensive income (loss), net of tax	377	162
AOCI ending balance	497	172
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(143)	(8)
Other comprehensive income (loss) before reclassifications	1	(84)
Net realized (gains) losses reclassified from AOCI into earnings	0	0
Other comprehensive income (loss), net of tax	1	(84)
AOCI ending balance	(142)	(92)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(30)	(21)
Other comprehensive income (loss) before reclassifications	(13)	(1)
Net realized (gains) losses reclassified from AOCI into earnings	2	(1)
Other comprehensive income (loss), net of tax	(11)	(2)
AOCI ending balance	$ (41)	$ (23)