Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Parenthetical) (Detail) (USD $)	3 Months Ended
Mar. 31, 2011
Earnings Per Common Share [Line Items]
Amortization of discount on preferred stock including deemed dividend	$ 49,000,000
Series B Preferred Stock [Member]
Earnings Per Common Share [Line Items]
Repurchase of the Fixed-Rate Perpetual Preferred Stock	$ 2,500,000,000

One-time deemed dividend related to the remaining difference between the repurchase price and the carrying value of the preferred shares at the time of repurchase.

No definition available.

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