Asset Quality - Concession Types for our Commercial Accruing and Nonaccruing TDRs (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Receivables [Abstract]
Additional funds to borrowers related to lending related commitments	$ 26	$ 32	$ 47

Significant commitments to lend additional funds to borrowers with loans on nonperforming status.

No definition available.

Name:	key_SignificantCommitmentsToLendAdditionalFundsToBorrowersWithLoansOnNonperformingStatus
Namespace Prefix:	key_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant