Derivatives and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 80
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	347
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	410
Reclassify of net losses on derivative instruments from AOCI	19
Length of time hedge in cash flow hedge	12 months
Reclassification of net gains related to terminated cash flow hedges from AOCI to income	4
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	4
Cash collateral netted against derivative assets	270	308	440
Collateral netted against derivative liabilities	5	4	21
Cash collateral not netted transferred with clearing organization	26
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	468
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	82
Over-collateralization on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	3
Additional collateral held in the form of securities	85
Default reserve associated with uncollateralized contracts	13	14
Gross exposure on derivatives after taking into account effects of master netting agreements	389
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	345
Net liability position totaled	108	106	169
Cash and securities collateral posted	43	42	58
Maximum [Member]
Credit Derivatives [Line Items]
Derivative liabilities after effects of bilateral collateral and master netting agreements	2
KeyBank (consolidated) [Member]
Credit Derivatives [Line Items]
Net liability position totaled	342
Derivative assets included in net liability position	274
Derivative liabilities included in net liability position	616
Cash and securities collateral posted	344
Payments to terminate contracts	13
Key Corp [Member]
Credit Derivatives [Line Items]
Net liability position totaled	2
Payments to terminate contracts	2
Key Corp [Member] | Maximum [Member]
Credit Derivatives [Line Items]
Cash and securities collateral posted	1
Additional collateral amount	$ 2	$ 1	$ 3