Trust Preferred Securities Issued by Unconsolidated Subsidiaries - Summary of Trust Preferred Securities, Common Stock and Related Debentures (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Stock	$ 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	1.10%
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	113
Common Stock	4
Principal Amount of Debentures, Net of Discount	117
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	148
Common Stock	4
Principal Amount of Debentures, Net of Discount	152
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	417	1,206
Common Stock	14	19
Principal Amount of Debentures, Net of Discount	$ 431	$ 1,225
Interest Rate of Trust Preferred Securities and Debentures	5.025%	6.61%