Derivatives and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 137
Derivative liabilities 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	472
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	604
Reclassify of net losses on derivative instruments from AOCI	35
Length of time hedge in cash flow hedge	12 months
Reclassification of net gains related to terminated cash flow hedges from AOCI to income	5
Maximum length of time over which forecasted transactions are hedged, years	15 years
Other Comprehensive income unrealized loss on derivatives arising during period net of tax	2
Cash collateral netted against derivative assets	440	494	450
Collateral netted against derivative liabilities	21	27	2
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	741
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	129
Net exposure on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	12
Additional collateral held in the form of securities	141
Default reserve associated with uncollateralized contracts	17	19
Gross exposure on derivatives after taking into account effects of master netting agreements	533
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	480
Net liability position totaled	169	191	233
Cash and securities collateral posted	58	66	57
KeyBank [Member]
Credit Derivatives [Line Items]
Net liability position totaled	457
Derivative assets included in net liability position	435
Derivative liabilities included in net liability position	892
Cash and securities collateral posted	441
Payments to terminate contracts	13
Key Corp [Member]
Credit Derivatives [Line Items]
Net liability position totaled	21
Derivative liabilities included in net liability position	21
Cash and securities collateral posted	19
Additional collateral amount	3	3
Payments to terminate contracts	$ 3