Trust Preferred Securities Issued by Unconsolidated Subsidiaries (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Stock	$ 1,257	$ 1,257
Debentures adjustments related to financial instrument hedging	13	17
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 Debentures, Net of Discount	$ 162
Interest Rate of Trust Preferred Securities and Debentures	5.494%
KeyCorp Capital I | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
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	$ 86
Common Stock	4
Principal Amount of Debentures, Net of Discount	$ 90
Interest Rate of Trust Preferred Securities and Debentures	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	$ 112
Common Stock	4
Principal Amount of Debentures, Net of Discount	$ 116
Interest Rate of Trust Preferred Securities and Debentures	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	$ 21
Common Stock	1
Principal Amount of Debentures, Net of Discount	$ 22
Interest Rate of Trust Preferred Securities and Debentures	6.793%
HNC Statutory Trust III | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.40%
HNC Statutory Trust IV
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 18
Common Stock	1
Principal Amount of Debentures, Net of Discount	$ 19
Interest Rate of Trust Preferred Securities and Debentures	6.579%
HNC Statutory Trust IV | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.28%
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 Debentures, Net of Discount	$ 21
Interest Rate of Trust Preferred Securities and Debentures	6.862%
Willow Grove Statutory Trust I | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	1.31%
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 Debentures, Net of Discount	$ 8
Interest Rate of Trust Preferred Securities and Debentures	7.70%
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 Debentures, Net of Discount	$ 8
Interest Rate of Trust Preferred Securities and Debentures	7.70%
Total
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust Preferred Securities, Net of Discount	$ 429	433
Common Stock	17	17
Principal Amount of Debentures, Net of Discount	$ 446	$ 450
Interest Rate of Trust Preferred Securities and Debentures	6.616%	5.321%
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 | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Basis spread on variable rate	2.19%