Securities - Available for Sale Securities (Unrealized Loss Position) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Available For Sale Securities [Abstract]
Gross unrealized losses	$ 1	$ 1	$ 1

Securities continuous unrealized loss position aggregate losses.

No definition available.

Name:	key_SecuritiesContinuousUnrealizedLossPositionAggregateLosses
Namespace Prefix:	key_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant