Income Taxes - Effective tax rates (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income tax reconciliation
Tax expense (benefit) at the U.S. federal statutory income tax rate										$ (206)	$ 57	$ 123
State and local taxes, net of federal benefit										(2)	23	40
Adjustment of Federal tax rate used to value deferred taxes	[1]									0	0	(31)
Non-deductible FDIC assessment fees										15	5	27
Non-deductible goodwill impairment	[2]									165	77	0
Other non-deductible / non-taxable items	[3]									9	0	107
Items affecting prior periods	[4]									3	7	(1)
Uncertain tax positions										(8)	5	6
Low income housing and other tax credit investments										(14)	(13)	(5)
Other										(4)	(4)	0
Total income tax expense (benefit)		$ 30	$ 36	$ 49	$ (157)	$ 48	$ 39	$ 35	$ 35	$ (42)	$ 157	$ 266
Effective income tax reconciliation
Tax expense (benefit) at the U.S. federal statutory income tax rate, percentage										(21.00%)	21.00%	21.00%
State and local taxes, net of federal benefit, percentage										(0.20%)	8.50%	6.80%
Adjustment of Federal tax rate used to value deferred taxes, percentage	[1]									0.00%	0.00%	(5.30%)
Non-deductible FDIC assessment fees, percent										1.50%	1.90%	4.60%
Non-deductible goodwill impairment, percent	[2]									16.80%	28.50%	0.00%
Other non-deductible / non-taxable items, percentage	[3]									0.90%	0.00%	18.30%
Items affecting prior periods, percentage	[4]									0.30%	2.60%	(0.20%)
Uncertain tax positions, percentage										(0.80%)	1.90%	1.10%
Low income housing and other tax credit investments, percentage										(1.40%)	(4.80%)	(0.90%)
Other, percentage										(0.40%)	(1.50%)	0.00%
Effective tax rate, percentage										(4.30%)	58.10%	45.40%

[1] The amount primarily relates to tax return adjustments on certain deferred tax assets impacted by the change in the Federal corporate income tax rate.

[2] For 2020, the amount represents non-deductible goodwill impairment related to our previously separate Retail Banking and Wealth Management and Private Banking businesses. For 2019, the amount represents non-deductible goodwill impairment related to our previously separate Retail Banking and Wealth Management business.

[3] The amounts primarily relate to non-deductible penalties related to legal matters.

[4] For 2020, the amount primarily relates to prior year State audit settlements, partially offset by changes in estimates as a result of filing the 2019 Federal and State income tax returns. For 2019, the amount primarily relates to changes in estimates as a result of filing the 2018 Federal income tax return and a reduction in a State and local capital loss carryback claim, partially offset by prior year State audit adjustments