Asset Quality - Past Due Loans Including Current Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012	Dec. 31, 2012
Receivables [Abstract]
Performing home equity second liens including nonperforming loans	$ 38	$ 72

Performing secured loans discharged through bankruptcy.

No definition available.

Name:	key_PerformingSecuredLoansDischargedThroughBankruptcy
Namespace Prefix:	key_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration