Stockholders' Equity - Change in AOCI Gain (Loss) by Component (Net of Tax) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	$ (430)	$ (872)
Other comprehensive income (loss) before reclassifications	234	176
Net realized (gains) losses reclassified from AOCI into earnings	(16)	(14)
Other comprehensive income, net of tax	218	162
AOCI ending balance	(212)	(710)
Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	410	106
Other comprehensive income (loss) before reclassifications	114	149
Net realized (gains) losses reclassified from AOCI into earnings	8	(5)
Other comprehensive income, net of tax	122	144
AOCI ending balance	532	250
Accumulated Net Unrealized Investment Gain (Loss) | Securities Held to Maturity
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(821)	(897)
Other comprehensive income (loss) before reclassifications	0	0
Net realized (gains) losses reclassified from AOCI into earnings	20	13
Other comprehensive income, net of tax	20	13
AOCI ending balance	(801)	(884)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	10	(110)
Other comprehensive income (loss) before reclassifications	205	40
Net realized (gains) losses reclassified from AOCI into earnings	(43)	(21)
Other comprehensive income, net of tax	162	19
AOCI ending balance	172	(91)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(8)	40
Other comprehensive income (loss) before reclassifications	(84)	(13)
Net realized (gains) losses reclassified from AOCI into earnings	0	0
Other comprehensive income, net of tax	(84)	(13)
AOCI ending balance	(92)	27
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(21)	(11)
Other comprehensive income (loss) before reclassifications	(1)	0
Net realized (gains) losses reclassified from AOCI into earnings	(1)	(1)
Other comprehensive income, net of tax	(2)	(1)
AOCI ending balance	$ (23)	$ (12)