Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
EARNINGS
Income (loss) from continuing operations		$ 530	$ 724	$ 977	$ 1,342
Less: Net income (loss) attributable to noncontrolling interests		0	0	0	0
Income (loss) from continuing operations attributable to Key		530	724	977	1,342
Less: Dividends on Preferred Stock		26	26	53	53
Income (loss) from continuing operations attributable to Key common shareholders		504	698	924	1,289
Income (loss) from discontinued operations, net of taxes		3	5	4	9
Net income (loss) attributable to Key common shareholders		$ 507	$ 703	$ 928	$ 1,298
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average common shares outstanding (000) (in shares)		924,302	957,423	923,717	961,292
Effect of common share options and other stock awards (in shares)		7,506	9,740	9,087	9,514
Weighted-average common shares and potential common shares outstanding (in shares)	[1]	931,808	967,163	932,805	970,806
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders (in usd per share)		$ 0.54	$ 0.73	$ 1.00	$ 1.34
Income (loss) from discontinued operations, net of taxes (in usd per share)		0	0	0	0.01
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	0.55	0.73	1.00	1.35
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution (in usd per share)		0.54	0.72	0.99	1.33
Income (loss) from discontinued operations, net of taxes - assuming dilution (in usd per share)		0	0	0	0.01
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	$ 0.54	$ 0.73	$ 1.00	$ 1.34

[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.