Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011		Dec. 31, 2011
Unrealized gains on securities available-for-sale, not other-than temporarily impaired:
Balance at beginning of period	$ 1,004	$ 239	$ 883	$ 97
Other comprehensive income for period:
Net unrealized holding gains arising during period, net of tax	126	683	303	858
Reclassification adjustment for gains realized in net income, net of tax	(29)	(28)	(85)	(61)
Total other comprehensive income for period	97	655	218	797
Balance at end of period	1,101	894	1,101	894
Unrealized gains (losses) on other-than-temporarily impaired debt securities available-for-sale:
Balance at beginning of period				(1)
Other comprehensive income for period:
Reclassification adjustment for losses realized in net income, net of tax of less than $1 million				1
Total other comprehensive income (loss) for period				1	[1]
Unrealized gains (losses) on other-than-temporarily impaired debt securities held-to-maturity:
Balance at beginning of period				(153)
Other comprehensive income for period:
Net unrealized other-than-temporary impairment arising during period				11
Adjustment to reverse other-than-temporary impairment due to deconsolidation of VIE				142
Total other comprehensive income for period				153
Unrealized losses on derivatives designated as cash flow hedges:
Balance at beginning of period	(229)	(104)	(229)	(87)
Other comprehensive income (loss) for period:
Net gains (losses) arising during period, net of tax	9	(126)	4	(146)
Reclassification adjustment for losses realized in net income, net of tax	2	2	7	5
Total other comprehensive income (loss) for period	11	(124)	11	(141)
Balance at end of period	(218)	(228)	(218)	(228)
Pension and postretirement benefit liability:
Balance at beginning of period	(11)	(7)	(12)	(9)
Balance at end of period	(11)	(7)	(11)	(7)
Total accumulated other comprehensive income at end of period	872	659	872	659		642
Other comprehensive income for period:
Amortization of prior service cost and transition obligation included in net income, net of tax of less than $1 million in 2012 and 2011			1	2
Total other comprehensive income for period			1	2
Balance at end of period	(11)	(7)	(11)	(7)
Total accumulated other comprehensive income at end of period	$ 872	$ 659	$ 872	$ 659		$ 642

[1] During the three and nine months ended September 30, 2012 and 2011, there were no other-than-temporary impairment ("OTTI") losses on securities recognized in other revenues and no OTTI losses in the non-credit component on securities were recognized in accumulated other comprehensive income.