Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Disclosure Asset Quality Changes In Allowance For Loan And Lease Losses By Loan Category [Abstract]
Foreign currency translation adjustment	$ 1	$ 1

Financing receivable allowance for credit losses foreign currency translation adjustment.

No definition available.

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