Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019
Income Tax Contingency [Line Items]
Total income tax expense (benefit), rate	12.50%	14.50%
Combined federal and state statutory tax rate			23.70%
Valuation allowance	$ 0		$ 0	$ 0
Other Assets
Income Tax Contingency [Line Items]
Net deferred tax liability	110,000,000		110,000,000	$ 89,000,000
Key Corp
Income Tax Contingency [Line Items]
Unrecognized tax benefits	58,000,000		58,000,000
First Niagara Bank, N.A.
Income Tax Contingency [Line Items]
Allocated bad debt deductions	$ 92,000,000		$ 92,000,000