Accumulated Other Comprehensive Income (Loss) - (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Unrealized gains (losses) on investment securities:
Balance at beginning of period	$ 287		$ 257		$ (18)		$ 992
Other comprehensive income for period:
Net unrealized gains (losses) arising during period, net of tax	(71)		(29)		243		(679)
Reclassification adjustment for gains realized in net income, net of tax	(17)	[1]	(21)	[1]	(26)	[1]	(106)	[1]
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income, net of tax	1	[2]	0	[2]	1	[2]	0	[2]
Total other comprehensive income (loss) for period	(87)		(50)		218		(785)
Balance at end of period	200		207		200		207
Unrealized losses on other-than-temporarily impaired debt securities held-to-maturity:
Balance at beginning of period	(57)		(67)		(60)		0
Other comprehensive income for period:
Adjustment to add other-than-temporary impairment due to the consolidation of a VIE, net of tax					0		(67)
Reclassification adjustment related to the accretion of unrealized other-than-temporary impairment, net of tax	6	[3]	2	[3]	9	[3]	2	[3]
Total other comprehensive income for period	6		2		9		2
Balance at end of period	(51)		(65)		(51)		(65)
Unrealized (losses) gains on derivatives classified as cash flow hedges:
Balance at beginning of period	(118)		(127)		(83)		(201)
Other comprehensive income (loss) for period:
Net gains (losses) arising during period, net of tax	(6)		20		(42)		90
Reclassification adjustment for losses realized in net income, net of tax	1	[4]	1	[4]	2	[4]	5	[4]
Total other comprehensive income (loss) for period	(5)		21		(40)		95
Balance at end of period	(123)		(106)		(123)		(106)
Pension and postretirement benefit liability:
Balance at beginning of period	2		(6)		2		(6)
Other comprehensive income for period:
Change in unfunded pension liability arising during the period, net of tax	0		1		0		1
Total other comprehensive income (loss) for period	0		1		0		1
Balance at end of period	2		(5)		2		(5)
Total accumulated other comprehensive income at end of period	$ 28		$ 31		$ 28		$ 31		$ (159)

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

[2] Amount amortized to net income is included in interest income in our consolidated statement of income. During the third quarter of 2014, we transferred securities from available-for-sale to held-to-maturity. At the date of the transfer, AOCI included net pretax unrealized losses of $234 million related to the transferred securities which will be amortized over the remaining contractual life of each security as an adjustment of yield in a manner consistent with the amortization of any premium or discount.

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

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