Derivatives and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 Counterparty	Dec. 31, 2014	Mar. 31, 2014
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 93,000,000
Derivative liabilities after effects of bilateral collateral and master netting agreements	25,000,000
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	638,000,000
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	850,000,000
Reclassify of net losses on derivative instruments from AOCI	29,000,000
Length of time hedge in cash flow hedge	12 months
Reclassification of net gains related to terminated cash flow hedges from AOCI to income	2,000,000
Maximum length of time over which forecasted transactions are hedged, years	13 years
Other Comprehensive income unrealized gain on derivatives arising during period net of tax	33,000,000
Cash collateral netted against derivative assets	514,000,000	518,000,000	270,000,000
Collateral netted against derivative liabilities	31,000,000	26,000,000	5,000,000
Cash collateral not netted transferred with clearing organization	68,000,000
Cash collateral not netted transferred from clearing organization	7,000,000
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	946,000,000
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	243,000,000
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	74,000,000
Additional collateral held in the form of securities	169,000,000
Default reserve associated with uncollateralized contracts	8,000,000	9,000,000
Gross exposure on derivatives after taking into account effects of master netting agreements	550,000,000
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	488,000,000
Letter of credit	35,000,000
Number of counter parties guaranteed	1
Key Corp [Member]
Credit Derivatives [Line Items]
Net liability position totaled	9,000,000
Cash and securities collateral posted	9,000,000
Key Corp [Member] | Maximum [Member]
Credit Derivatives [Line Items]
Additional collateral amount		1,000,000	2,000,000
Key Corp [Member] | Maximum [Member] | Unsecured Debt [Member]
Credit Derivatives [Line Items]
Payments to terminate contracts	1,000,000
KeyBank (consolidated) [Member]
Credit Derivatives [Line Items]
Net liability position totaled	292,000,000
Derivative assets included in net liability position	276,000,000
Derivative liabilities included in net liability position	568,000,000
Cash and securities collateral posted	259,000,000
Number of ratings above noninvestment	4
KeyBank (consolidated) [Member] | Maximum [Member] | Unsecured Debt [Member]
Credit Derivatives [Line Items]
Payments to terminate contracts	$ 8,000,000