Derivatives and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Credit Derivatives [Line Items]
Derivative assets after effects of bilateral collateral and master netting agreements	$ 102
Derivative assets not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	373
Derivative liabilities not designated as hedging instruments after effects of bilateral collateral and master netting agreements, and a reserve for potential future losses	465
Reclassify of net losses on derivative instruments from AOCI	26
Length of time hedge in cash flow hedge	12 months
Reclassification of net gains related to terminated cash flow hedges from AOCI to income	6
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	327	494	503
Collateral netted against derivative liabilities	17	27	32
Cash collateral not netted transferred with clearing organization	9
Gross exposure on derivatives, after taking into account the effects of bilateral collateral and master netting agreements	584
Net exposure on derivatives, after taking into account, the effects of bilateral collateral and master netting agreements	121
Net exposure on derivatives to broker-dealers and banks, after the application of master netting agreements and collateral	20
Additional collateral held in the form of securities	101
Default reserve associated with uncollateralized contracts	12	19
Gross exposure on derivatives after taking into account effects of master netting agreements	400
Net exposure on derivatives with clients after application of master netting agreements collateral and related reserve	354
Net liability position totaled	123	191	216
Cash and securities collateral posted	44	66	67
Maximum [Member]
Credit Derivatives [Line Items]
Derivative liabilities after effects of bilateral collateral and master netting agreements	15
KeyBank [Member]
Credit Derivatives [Line Items]
Net liability position totaled	376
Derivative assets included in net liability position	339
Derivative liabilities included in net liability position	715
Cash and securities collateral posted	375
Payments to terminate contracts	13
Key Corp [Member]
Credit Derivatives [Line Items]
Net liability position totaled	7
Derivative liabilities included in net liability position	7
Cash and securities collateral posted	5
Additional collateral amount	2	3	3
Payments to terminate contracts	$ 2