Trust Preferred Securities Issued by Unconsolidated Subsidiaries - Summary of Trust Preferred Securities, Common Stock and Related Debentures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Stock	$ 1,257	$ 1,257
Debentures adjustments related to financial instrument hedging	52	70
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	0.871%
KeyCorp Capital II
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	6.875%
KeyCorp Capital III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 116
Common Stock	4
Principal Amount of of Debentures, Net of Discount	$ 120
Interest Rate of Trust Preferred Securities and Debentures	7.75%
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	1.57%
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	1.412%
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	1.513%
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	2.404%
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	2.404%
Business Trusts
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 466	483
Common Stock	17	17
Principal Amount of of Debentures, Net of Discount	$ 483	$ 500
Interest Rate of Trust Preferred Securities and Debentures	4.271%	4.464%
Treasury Rate | KeyCorp Capital II
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	20.00%
Treasury Rate | KeyCorp Capital III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	25.00%
London Interbank Offered Rate (LIBOR) | KeyCorp Capital I
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	74.00%
London Interbank Offered Rate (LIBOR) | HNC Statutory Trust III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	140.00%
London Interbank Offered Rate (LIBOR) | Willow Grove Statutory Trust I
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	131.00%
London Interbank Offered Rate (LIBOR) | HNC Statutory Trust IV
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	128.00%
London Interbank Offered Rate (LIBOR) | Westbank Capital Trust II and III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	219.00%
Debt Instrument, Redemption, Period Five | Treasury Rate | Keycorp Capital II and III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	50.00%