Trust Preferred Securities Issued by Unconsolidated Subsidiaries - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Trust Preferred Securities [Abstract]
Percentage of trust preferred securities issued by the KeyCorp of Tier 1 capital	0.90%
Trust preferred securities issued by the KeyCorp of Tier 1 capital	$ 85

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