Income Taxes - Income Taxes Included in Income Statement (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Income tax (benefit) expense on securities transactions		$ 0.4	$ 5.0
Equity and gross receipts based taxes assessed in lieu of income tax recorded in noninterest expense	$ 29	$ 21	$ 19

Income Tax Benefit Expense On Securities Transactions

No definition available.

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