Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Unrealized gains on securities available-for-sale, not other-than temporarily impaired:
Balance at beginning of period	$ 756	$ (51)	$ 883	$ 97
Other comprehensive income for period:
Net unrealized holding gains arising during period, net of tax of $203 million and $198 million, respectively	286	297	177	175
Reclassification adjustment for gains realized in net income, net of tax of $(27) million and $(5) million, respectively	(38)	(7)	(56)	(33)
Total other comprehensive (loss) for period	248	290	121	142
Balance at end of period	1,004	239	1,004	239
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
Balance at end of period
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
Balance at end of period
Unrealized losses on derivatives classified as cash flow hedges:
Balance at beginning of period	(192)	(90)	(229)	(87)
Other comprehensive loss for period:
Net losses arising during period, net of tax of $(29) million and $(25) million, respectively	(39)	(15)	(5)	(20)
Reclassification adjustment for losses realized in net income, net of tax of $(2) million and $(1) million, respectively	2	1	5	3
Total other comprehensive income (loss) for period	(37)	(14)		(17)
Balance at end of period	(229)	(104)	(229)	(104)
Pension and postretirement benefit liability:
Balance at beginning of period	(11)	(8)	(12)	(9)
Other comprehensive income (loss) for period:
Change in unfunded pension postretirement liability, net of tax of less than $1 million in 2012 and 2011		1	1	2
Amortization of prior service cost and transition obligation included in net income, net of tax of less than $1 million in 2012 and 2011
Total other comprehensive income for period		1	1	2
Balance at end of period	(11)	(7)	(11)	(7)
Total accumulated other comprehensive income at end of period	$ 764	$ 128	$ 764	$ 128	$ 642