Income Taxes Income Taxes - Net Deferred Tax Position (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Allowance for credit losses	$ 267	$ 369
Benefit accruals	120	147
Accrued expenses not currently deductible	247	315
Tax credit carry-forwards	0	145
Interest and discount income	230	74
Future benefit of state reserves	161	140
REMIC losses not currently deductible	188	130
Other	463	482
Total deferred tax assets	1,676	1,802
Less deferred tax liabilities:
Fair value adjustments	10	172
Unrealized gains (losses) on available-for-sale securities	692	606
Mortgage servicing rights	69	85
Total deferred tax liabilities	771	863
Net deferred tax asset	$ 905	$ 939