Trust Preferred Securities Issued by Unconsolidated Subsidiaries - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Trust Preferred Securities [Abstract]
Percentage of trust preferred securities issued by the KeyCorp of Tier 1 capital	3.40%
Trust preferred securities issued by the KeyCorp of Tier 1 capital	$ 340

Percentage of capital securities issued by company and union state bank capital trusts of tier one capital.

No definition available.

Name:	key_PercentageOfCapitalSecuritiesIssuedByCompanyAndUnionStateBankCapitalTrustsOfTierOneCapital
Namespace Prefix:	key_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant