Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Income Tax Contingency [Line Items]
Total income tax expense (benefit), rate	14.00%	16.80%
Combined federal and state statutory tax rate			23.70%
Federal deferred tax asset	$ (177,000,000)		$ (177,000,000)	$ (89,000,000)
Valuation allowance	0		0	$ 0
Key Corp
Income Tax Contingency [Line Items]
Unrecognized tax benefits	18,000,000		18,000,000
First Niagara Bank, N.A.
Income Tax Contingency [Line Items]
Allocated bad debt deductions	$ 92,000,000		$ 92,000,000