Income Taxes - Effective tax rates (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended								12 Months Ended
		Dec. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax reconciliation
Tax expense (benefit) at the U.S. federal statutory income tax rate											$ 57	$ 123	$ 367
State and local taxes, net of federal benefit											23	40	28
Adjustment of Federal tax rate used to value deferred taxes	[1]										0	(31)	865
Adjustment of State tax rate used to value deferred taxes	[2]										0	2	(15)
Non-deductible FDIC assessment fees											5	27	0
Non-deductible goodwill impairment	[3]										77	0	0
Other non-deductible / non-taxable items	[4]										0	107	1
Items affecting prior periods	[5]										7	(1)	6
Uncertain tax positions											5	6	0
Low income housing and other tax credit investments											(13)	(5)	(17)
Stock based compensation											(2)	(2)	(8)
Other											(2)	0	1
Total income tax expense (benefit)			$ 48	$ 39	$ 35	$ 35	$ 34	$ 58	$ 82	$ 92	$ 157	$ 266	1,228
Out of period adjustment to deferred tax assets													$ (9)
Effective income tax reconciliation
Tax expense (benefit) at the U.S. federal statutory income tax rate, percentage		35.00%									21.00%	21.00%	35.00%
State and local taxes, net of federal benefit, percentage											8.50%	6.80%	2.70%
Adjustment of Federal tax rate used to value deferred taxes, percentage	[1]										0.00%	(5.30%)	82.40%
Adjustment of State tax rate used to value deferred taxes, percentage	[2]										0.00%	0.30%	(1.40%)
Non-deductible FDIC assessment fees, percent											1.90%	4.60%	0.00%
Non-deductible goodwill impairment, percent	[3]										28.50%	0.00%	0.00%
Other non-deductible / non-taxable items, percentage	[4]										0.00%	18.30%	0.10%
Items affecting prior periods, percentage	[5]										2.60%	(0.20%)	0.60%
Uncertain tax positions, percentage											1.90%	1.00%	0.00%
Low income housing and other tax credit investments, percentage											(4.80%)	(0.90%)	(1.60%)
Stock-based compensation, percentage											(0.70%)	(0.20%)	(0.80%)
Other, percentage											(0.80%)	0.00%	0.10%
Effective tax rate, percentage											58.10%	45.40%	117.10%

[1] For 2018, the amount primarily relates to tax return adjustments on certain deferred tax assets impacted by the Federal tax rate change. For 2017, the amount relates to the effects of revaluing our net deferred tax asset for new Tax Legislation that was enacted in December 2017.

[2] For 2017, the amount includes an out of period adjustment to our deferred tax asset balance which decreased tax expense by $9 million.

[3] Represents non-deductible goodwill impairment related to our Retail Banking and Wealth Management reporting unit in 2019.

[4] For 2018, the amount primarily relates to non-deductible penalties related to legal matters.

[5] 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. For 2017, the amount relates to the impact of adjustments associated with filing the 2016 State income tax returns and changes in tax credits as a result of filing the 2016 Federal income tax return.