Income Taxes - Effective tax rates (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Income tax reconciliation
Tax expense (benefit) at the U.S. federal statutory income tax rate	$ 100		$ 34
State and local taxes, net of federal benefit	17		6
Adjustment of tax rate used to value deferred taxes	2		(10)
Validation of tax accounts	(10)		0
Accrual of tax reserves	14	[1]	16	[1]
Tax exempt interest income	(3)		(2)
Low income housing and other tax credits	(18)		(25)
Other	2		(1)
Total	$ 104		$ 18
Effective income tax reconciliation
Tax expense (benefit) at the U.S. federal statutory income tax rate, percentage	35.00%		35.00%
State and local taxes, net of federal benefit, percentage	5.90%		6.10%
Adjustment of tax rate used to value deferred taxes, percentage	0.60%		(10.20%)
Validation of tax accounts	(3.50%)		0.00%
Accural of tax reserves, percentage	4.90%	[1]	16.30%	[1]
Tax exempt interest income, percentage	(1.00%)		(2.00%)
Low income housing and other tax credits, percentage	(6.30%)		(25.60%)
Other, percentage	0.60%		(1.20%)
Effective tax rate, percentage	36.20%		18.40%

[1] eserves in 2013 and 2012 relate to state uncertain tax positions which we no longer believe we meet the more likely than not requirement for recognition.