Derivatives and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Counterparty	Dec. 31, 2013
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 55
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	554
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	794
Reclassify of net losses on derivative instruments from AOCI	25
Length of time hedge in cash flow hedge	12 months
Reclassification of net gains related to terminated cash flow hedges from AOCI to income	3
Maximum length of time over which forecasted transactions are hedged, years	14 years
Other Comprehensive income unrealized gain on derivatives arising during period net of tax	17
Cash collateral netted against derivative assets	518	308
Collateral netted against derivative liabilities	26	4
Cash collateral not netted transferred with clearing organization	56
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	955
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	204
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	23
Additional collateral held in the form of securities	181
Default reserve associated with uncollateralized contracts	9	14
Gross exposure on derivatives after taking into account effects of master netting agreements	471
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	405
Letter of credit	30
Number of counter parties guaranteed	1
Net liability position totaled	31	106
Cash and securities collateral posted	100	42
Maximum [Member]
Credit Derivatives [Line Items]
Derivative liabilities after effects of bilateral collateral and master netting agreements	10
KeyBank (consolidated) [Member]
Credit Derivatives [Line Items]
Net liability position totaled	297
Derivative assets included in net liability position	175
Derivative liabilities included in net liability position	472
Cash and securities collateral posted	243
Payments to terminate contracts	5
Key Corp [Member]
Credit Derivatives [Line Items]
Net liability position totaled	7
Payments to terminate contracts	1
Key Corp [Member] | Maximum [Member]
Credit Derivatives [Line Items]
Cash and securities collateral posted	7
Additional collateral amount	$ 1	$ 1