Trust Preferred Securities Issued by Unconsolidated Subsidiaries (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Stock	$ 1,257	$ 1,257
Debentures adjustments related to financial instrument hedging	29	52
KeyCorp Capital I
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	156
Common Stock	6
Principal amount of of debentures, net of discount	$ 162
Interest rate of Trust preferred securities and debentures (as a percent)	1.707%
KeyCorp Capital I | London Interbank Offered Rate (LIBOR)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.74%
KeyCorp Capital II
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 93
Common Stock	4
Principal amount of of debentures, net of discount	$ 97
Interest rate of Trust preferred securities and debentures (as a percent)	6.875%
KeyCorp Capital II | Treasury Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.20%
KeyCorp Capital III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 121
Common Stock	4
Principal amount of of debentures, net of discount	$ 125
Interest rate of Trust preferred securities and debentures (as a percent)	7.75%
KeyCorp Capital III | Treasury Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.25%
HNC Statutory Trust III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 20
Common Stock	1
Principal amount of of debentures, net of discount	$ 21
Interest rate of Trust preferred securities and debentures (as a percent)	2.905%
HNC Statutory Trust III | London Interbank Offered Rate (LIBOR)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.40%
Willow Grove Statutory Trust I
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 20
Common Stock	1
Principal amount of of debentures, net of discount	$ 21
Interest rate of Trust preferred securities and debentures (as a percent)	2.566%
Willow Grove Statutory Trust I | London Interbank Offered Rate (LIBOR)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.31%
HNC Statutory Trust IV
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 17
Common Stock	1
Principal amount of of debentures, net of discount	$ 18
Interest rate of Trust preferred securities and debentures (as a percent)	3.139%
HNC Statutory Trust IV | London Interbank Offered Rate (LIBOR)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.28%
Westbank Capital Trust II
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 8
Common Stock	0
Principal amount of of debentures, net of discount	$ 8
Interest rate of Trust preferred securities and debentures (as a percent)	4.253%
Westbank Capital Trust III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 8
Common Stock	0
Principal amount of of debentures, net of discount	$ 8
Interest rate of Trust preferred securities and debentures (as a percent)	4.253%
Business Trusts
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities, net of discount	$ 443	466
Common Stock	17	17
Principal amount of of debentures, net of discount	$ 460	$ 483
Interest rate of Trust preferred securities and debentures (as a percent)	4.682%	4.271%
Keycorp Capital II and III | Redemption upon either tax or a capital treatment event | Treasury Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	0.50%
Westbank Capital Trust II and III | London Interbank Offered Rate (LIBOR)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	2.19%