Derivatives and Hedging Activities - Additional Information (Details)		12 Months Ended
		Dec. 31, 2019 USD ($) derivative rating	Dec. 31, 2018 USD ($) rating	Dec. 31, 2017 USD ($)
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements		$ 65,000,000
Derivative liabilities after effects of bilateral collateral and master netting agreements		4,000,000
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses		715,000,000
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses		194,000,000
Reclassify of after-tax net losses on derivative instruments from AOCI		$ (132,000,000)
Length of time hedge in cash flow hedge		12 months
Reclassification of net losses related to terminated cash flow hedges from AOCI to income		$ (3,000,000)
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		$ 32,000,000
Other income	[1]	(68,000,000)	$ (176,000,000)	$ (153,000,000)
Cash collateral netted against derivative assets		207,000,000	33,000,000
Collateral netted against derivative liabilities		69,000,000	37,000,000
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements		431,000,000
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements		107,000,000
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral		105,000,000
Additional collateral held in the form of securities		2,000,000
Default reserve associated with uncollateralized contracts		27,000,000
Gross exposure on derivatives after taking into account effects of master netting agreements		753,000,000
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve		672,000,000
Net liability position totaled		$ 9,000,000	$ 1,000,000
Number of credit risk derivatives held | derivative		0
KeyBank (consolidated) [Member]
Credit Derivatives [Line Items]
Net liability position totaled		$ 62,000,000
Derivative assets included in net liability position		25,000,000
Derivative liabilities included in net liability position		87,000,000
Cash and securities collateral posted		$ 60,000,000
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		$ 3,000,000	$ 4,000,000
Key Corp [Member]
Credit Derivatives [Line Items]
Additional collateral held in the form of securities		0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign Currency Translation Adjustment [Member]
Credit Derivatives [Line Items]
Other income		$ 14,000,000	$ 0

[1] Net securities gains (losses) totaled $20 million for the year ended December 31, 2019, less than $1 million for the year ended December 31, 2018, and $1 million for the year ended December 31, 2017. For 2019, 2018, and 2017, we did not have any impairment losses related to securities.