Asset Quality - Past Due Loans Including Current Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Performing home equity second liens including nonperforming loans	$ 38

Performing Secured Loans Discharged Through Bankruptcy

No definition available.

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