Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
EARNINGS
Income (loss) from continuing operations		$ 286	$ 530	$ 597	$ 977
Less: Net income (loss) attributable to noncontrolling interests		0	0	0	0
Income (loss) from continuing operations attributable to Key		286	530	597	977
Less: Dividends on Preferred Stock		36	26	72	53
Income (loss) from continuing operations attributable to Key common shareholders		250	504	525	924
Income (loss) from discontinued operations, net of taxes		1	3	2	4
Net income (loss) attributable to Key common shareholders		$ 251	$ 507	$ 527	$ 928
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average Common Shares outstanding (in shares)		926,741	924,302	926,807	923,717
Effect of Common Share options and other stock awards (in shares)		3,713	7,506	5,513	9,087
Weighted-average Common Shares and potential Common Shares outstanding (in shares)	[1]	930,454	931,808	932,320	932,805
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders (in usd per share)		$ 0.27	$ 0.54	$ 0.57	$ 1.00
Income (loss) from discontinued operations, net of taxes (in usd per share)		0	0	0	0
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	0.27	0.55	0.57	1.00
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution (in usd per share)		0.27	0.54	0.56	0.99
Income (loss) from discontinued operations, net of taxes - assuming dilution (in usd per share)		0	0	0	0
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	$ 0.27	$ 0.54	$ 0.57	$ 1.00

[1] Assumes conversion of Common Share options and other stock awards and/or convertible preferred stock, as applicable.

[2] EPS may not foot due to rounding.