Income Taxes - Effective tax rates (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Income tax reconciliation
Tax expense at the U.S. federal statutory income tax rate	$ 80		$ (84)		$ 181		$ (50)
State and local taxes, net of federal benefit	13		16		30		22
Adjustment of tax rate used to value deferred taxes					0		(10)
Non-deductible expense accrual related to certain regulatory matters	0	[1]	245	[1]	0	[1]	245	[1]
Non-deductible goodwill related to branch sale	0	[1]	106	[1]	0	[1]	106	[1]
Other non-deductible / non-taxable items	(12)	[2]	(3)	[2]	(9)	[2]	(8)	[2]
Items affecting prior periods	(12)	[3]	33	[3]	(22)	[3]	33	[3]
Uncertain tax adjustments	4	[4]	49	[4]	18	[4]	65	[4]
Impact of foreign operations	1		35		4		21
Low income housing tax credits	(22)		(31)		(43)		(42)
Other	(3)		(15)		(6)		(13)
Total income tax expense	$ 49		$ 351		$ 153		$ 369
Effective income tax reconciliation
Tax expense at the U.S. federal statutory income tax rate, percentage	35.00%		(35.00%)		35.00%		(35.00%)
State and local taxes, net of federal benefit, percentage	5.70%		6.60%		5.80%		15.30%
Non-deductible expense accrual related to certain regulatory matters, percentage	0.00%	[1]	101.20%	[1]	0.00%	[1]	170.10%	[1]
Adjustment of tax rate used to value deferred taxes, percentage					0.00%		(6.90%)
Non-deductible goodwill related to branch sale, percentage	0.00%	[1]	43.80%	[1]	0.00%	[1]	73.60%	[1]
Other non-deductible / non-taxable items, percentage	(5.20%)	[2]	(1.20%)	[2]	(1.70%)	[2]	(5.60%)	[2]
Items affecting prior periods, percentage	(5.20%)	[3]	13.60%	[3]	(4.30%)	[3]	22.90%	[3]
Impact of foreign operations, percentage	0.40%		14.50%		0.80%		14.60%
Uncertain tax adjustments, percentage	1.70%	[4]	20.20%	[4]	3.50%	[4]	45.10%	[4]
Low income housing tax credits, percentage	(9.70%)		(12.80%)		(8.30%)		(29.20%)
Other, percentage	(1.30%)		(5.90%)		(1.10%)		(8.60%)
Total income tax expense, percentage	21.40%		145.00%		29.70%		256.30%

[1] Relates to non-deductible expense related to certain regulatory matters and non-deductible goodwill related to the branches sold to First Niagara in 2012.

[2] Mainly relates to a change in the assessment of the deductibility of certain amounts accrued for certain regulatory matters.

[3] Relates to corrections to current and deferred tax balance sheet accounts.

[4] Reflects changes in state uncertain tax positions which no longer meet the more likely than not requirement for recognition.