Accumulated Other Comprehensive Income (Loss) - (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Sep. 30, 2014
Unrealized gains (losses) on investment securities:
Balance at beginning of period	$ (18)		$ 992		$ 883
Other comprehensive income for period:
Net unrealized gains (losses) arising during period, net of tax	244		(897)		194
Reclassification adjustment for gains realized in net income, net of tax	(74)	[1]	(113)	[1]	(85)	[1]
Amortization of net unrealized losses on securities transferred from available-for-sale to held-to-maturity realized in net income, net of tax	6	[2]	0	[2]	0	[2]
Total other comprehensive income (loss) for period	176		(1,010)		109
Balance at end of period	158		(18)		992
Unrealized losses on other-than-temporarily impaired debt securities held-to-maturity:
Balance at beginning of period	(60)		0		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)		0
Reclassification adjustment related to the accretion of unrealized other-than-temporary impairment, net of tax	9	[3]	7	[3]	0	[3]
Reclassification adjustment to reverse other-than-temporary impairment due to closure of VIE, net of tax of $36 million	51		0		0
Total other comprehensive income for period	60		7		0
Balance at end of period	0		(60)		0
Unrealized (losses) gains on derivatives classified as cash flow hedges:
Balance at beginning of period	(83)		(201)		(229)
Other comprehensive income (loss) for period:
Net gains (losses) arising during period, net of tax	(77)		112		18
Reclassification adjustment of losses realized in net income, net of tax	4	[4]	6	[4]	10	[4]
Total other comprehensive income (loss) for period	(73)		118		28
Balance at end of period	(156)		(83)		(201)
Pension and postretirement benefit liability:
Balance at beginning of period	2		(6)		(12)
Other comprehensive income for period:
Change in unfunded pension and postretirement liability, net of tax of $(4) million, $5 million and $4 million, respectively	(5)		8		4
Reclassification adjustment for prior service costs and transition obligation realized in net income, net of tax	0	[5]	0	[5]	2	[5]
Total other comprehensive income (loss) for period	(5)		8		6
Balance at end of period	(3)		2		(6)
Total accumulated other comprehensive income (loss) at end of period	(1)		(159)		785
AOCI included in pretax unrealized losses							$ (234)

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

[2] Amount amortized to net income (loss) is included in interest income in our consolidated statement of income (loss). 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 (loss) is included in interest income (expense) in our consolidated statement of income (loss).

[5] Amount reclassified to net income (loss) is included in salaries and employee benefits in our consolidated statement of income (loss).