Accumulated Other Comprehensive Income (Loss) - (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014	Sep. 30, 2014
Unrealized gains (losses) on investment securities:
Balance at beginning of period	$ 158		$ (18)
Other comprehensive income for period:
Net unrealized gains (losses) arising during period, net of tax	(19)		144
Reclassification adjustment for gains realized in net income, net of tax	(14)	[1]	(14)	[1]
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income, net of tax	5	[2]	0	[2]
Total other comprehensive income (loss) for period	(28)		130
Balance at end of period	130		112
Unrealized losses on other-than-temporarily impaired debt securities held-to-maturity:
Balance at beginning of period	0		(60)
Other comprehensive income for period:
Reclassification adjustment related to the accretion of unrealized other-than-temporary impairment, net of tax	0	[3]	1	[3]
Total other comprehensive income for period	0		1
Balance at end of period	0		(59)
Unrealized (losses) gains on derivatives classified as cash flow hedges:
Balance at beginning of period	(156)		(83)
Other comprehensive income (loss) for period:
Net unrealized losses arising during period, net of tax	(21)		(21)
Reclassification adjustment of losses realized in net income, net of tax	2	[4]	1	[4]
Total other comprehensive income (loss) for period	(19)		(20)
Balance at end of period	(175)		(103)
Pension and postretirement benefit liability:
Balance at beginning of period	(3)		2
Other comprehensive income for period:
Change in unfunded pension and postretirement liability, net of tax	1		0
Total other comprehensive income for period	1		0
Balance at end of period	(2)		2
Total accumulated other comprehensive loss at end of period	(47)		(48)		(1)
AOCI included in pretax unrealized losses						$ (234)

[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 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.