Accumulated Other Comprehensive Income - (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Unrealized gains (losses) on securities available-for-sale:
Balance at beginning of period	$ 112		$ 842		$ (18)		$ 992
Other comprehensive income for period:
Net unrealized gains (losses) arising during period, net of tax	171		(571)		315		(649)
Reclassification adjustment for gains realized in net income, net of tax	4	[1]	(14)	[1]	(10)	[1]	(86)	[1]
Total other comprehensive income (loss) for period	175		(585)		305		(735)
Balance at end of period	287		257		287		257
Unrealized losses on other-than-temporarily impaired debt securities held-to-maturity:
Balance at beginning of period	(59)		0		(60)		0
Adjustment to add other-than-temporary impairment due to the consolidation of a VIE, net of tax	0		(67)		0		(67)
Reclassification adjustment related to the accretion of unrealized other-than-temporary impairment, net of tax	2	[2]	0	[2]	3	[2]	0	[2]
Total other comprehensive income for period	2		0		3		0
Balance at end of period	(57)		(67)		(57)		(67)
Unrealized (losses) gains on derivatives classified as cash flow hedges:
Balance at beginning of period	(103)		(178)		(83)		(201)
Other comprehensive income (loss) for period:
Net gains (losses) arising during period, net of tax	(16)		49		(37)		70
Reclassification adjustment for losses realized in net income, net of tax	1	[3]	2	[3]	2	[3]	4	[3]
Total other comprehensive income (loss) for period	(15)		51		(35)		74
Balance at end of period	(118)		(127)		(118)		(127)
Pension and postretirement benefit liability:
Balance at beginning of period	2		(6)		2		(6)
Balance at end of period	2		(6)		2		(6)
Total accumulated other comprehensive income at end of period	$ 114		$ 57		$ 114		$ 57		$ (159)

[1] Amount reclassified to net income is included in other securities gains, net in our consolidated statement of income.

[2] Amount reclassified to the carrying value of the debt securities is included in securities held-to-maturity in our consolidated balance sheet.

[3] Amount reclassified to net income is included in interest income (expense) in our consolidated statement of income.