Derivatives and Hedging Activities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) derivative rating	Dec. 31, 2017 USD ($) rating
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 69,000,000
Derivative liabilities after effects of bilateral collateral and master netting agreements	(9,000,000)
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	462,000,000
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	395,000,000
Reclassify of after-tax net losses on derivative instruments from AOCI	$ 38,000,000
Length of time hedge in cash flow hedge	12 months
Reclassification of net losses related to terminated cash flow hedges from AOCI to income	$ 31,000,000
Maximum length of time over which forecasted transactions are hedged, years	10 years
Other Comprehensive income unrealized gain on derivatives arising during period net of tax	$ 27,000,000
Cash collateral netted against derivative assets	33,000,000	$ (23,000,000)
Collateral netted against derivative liabilities	37,000,000	150,000,000
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	382,000,000
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	241,000,000
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	237,000,000
Additional collateral held in the form of securities	4,000,000
Default reserve associated with uncollateralized contracts	4,000,000
Gross exposure on derivatives after taking into account effects of master netting agreements	345,000,000
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	290,000,000
Net liability position totaled	$ (1,000,000)	$ (3,000,000)
Number of credit risk derivatives held | derivative	0
KeyBank (consolidated) [Member]
Credit Derivatives [Line Items]
Net liability position totaled	$ 66,000,000
Derivative assets included in net liability position	80,000,000
Derivative liabilities included in net liability position	146,000,000
Cash and securities collateral posted	$ 55,000,000
KeyBank (consolidated) [Member] | Unsecured Debt [Member]
Credit Derivatives [Line Items]
Number of ratings above noninvestment | rating	4	4
KeyBank (consolidated) [Member] | Maximum [Member] | Unsecured Debt [Member]
Credit Derivatives [Line Items]
Payments to terminate contracts	$ 4,000,000	$ 12,000,000
Key Corp [Member]
Credit Derivatives [Line Items]
Additional collateral held in the form of securities	$ 0	$ 0