Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Disclosure Asset Quality Changes In Liability For Credit Losses On Lending Related Commitments [Abstract]
Balance at beginning of period	$ 29	$ 45
Provision (credit) for losses on lending-related commitments	3
Balance at end of period	$ 32	$ 45

Financing receivable allowance for credit losses liability.

No definition available.

Name:	key_FinancingReceivableAllowanceForCreditLossesLiability
Namespace Prefix:	key_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration