Stockholders' Equity - Change in AOCI Gain (Loss) by Component (Net of Tax) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	$ (397)	$ (371)	$ (430)	$ (872)
Other comprehensive income (loss) before reclassifications	268	(185)	327	336
Net realized (gains) losses reclassified from AOCI into earnings	(13)	(3)	(39)	(23)
Other comprehensive income, net of tax	255	(188)	288	313
AOCI ending balance	(142)	(559)	(142)	(559)
Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	366	419	410	106
Other comprehensive income (loss) before reclassifications	60	(67)	3	250
Net realized (gains) losses reclassified from AOCI into earnings	2	2	15	(2)
Other comprehensive income, net of tax	62	(65)	18	248
AOCI ending balance	428	354	428	354
Accumulated Net Unrealized Investment Gain (Loss) | Securities Held to Maturity
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(774)	(863)	(821)	(897)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Net realized (gains) losses reclassified from AOCI into earnings	25	22	72	56
Other comprehensive income, net of tax	25	22	72	56
AOCI ending balance	(749)	(841)	(749)	(841)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	91	(20)	10	(110)
Other comprehensive income (loss) before reclassifications	267	(39)	433	96
Net realized (gains) losses reclassified from AOCI into earnings	(37)	(29)	(122)	(74)
Other comprehensive income, net of tax	230	(68)	311	22
AOCI ending balance	321	(88)	321	(88)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(57)	106	(8)	40
Other comprehensive income (loss) before reclassifications	(52)	(82)	(101)	(16)
Net realized (gains) losses reclassified from AOCI into earnings	0	0	0	0
Other comprehensive income, net of tax	(52)	(82)	(101)	(16)
AOCI ending balance	(109)	24	(109)	24
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(23)	(13)	(21)	(11)
Other comprehensive income (loss) before reclassifications	(7)	3	(8)	6
Net realized (gains) losses reclassified from AOCI into earnings	(3)	2	(4)	(3)
Other comprehensive income, net of tax	(10)	5	(12)	3
AOCI ending balance	$ (33)	$ (8)	$ (33)	$ (8)