Trust Preferred Securities Issued by Unconsolidated Subsidiaries - Summary of Trust Preferred Securities, Common Stock and Related Debentures (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Stock	$ 1,017	$ 1,017	$ 1,017
KeyCorp Capital I [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	156
Common Stock	6
Principal Amount of Debentures, Net of Discount	162
Interest Rate of Trust Preferred Securities and Debentures	1.024%
Maturity of Trust Preferred Securities and Debentures	2028
KeyCorp Capital II [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	103
Common Stock	4
Principal Amount of Debentures, Net of Discount	107
Interest Rate of Trust Preferred Securities and Debentures	6.875%
Maturity of Trust Preferred Securities and Debentures	2029
KeyCorp Capital III [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	135
Common Stock	4
Principal Amount of Debentures, Net of Discount	139
Interest Rate of Trust Preferred Securities and Debentures	7.75%
Maturity of Trust Preferred Securities and Debentures	2029
Business Trusts [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	394	417	1,201
Common Stock	14	14	19
Principal Amount of Debentures, Net of Discount	$ 408	$ 431	$ 1,220
Interest Rate of Trust Preferred Securities and Debentures	4.858%	5.025%	6.616%