Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
EARNINGS
Income (loss) from continuing operations		$ 311	$ 447
Less: Net income (loss) attributable to noncontrolling interests		0	0
Income (loss) from continuing operations attributable to Key		311	447
Less: Dividends on Preferred Stock		36	27
Income (loss) from continuing operations attributable to Key common shareholders		275	420
Income (loss) from discontinued operations, net of taxes		1	1
Net income (loss) attributable to Key common shareholders		$ 276	$ 421
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average Common Shares outstanding (in shares)		926,490	922,941
Effect of Common Share options and other stock awards (in shares)		7,314	10,692
Weighted-average Common Shares and potential Common Shares outstanding (in shares)	[1]	933,804	933,634
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders (in usd per share)		$ 0.30	$ 0.45
Income (loss) from discontinued operations, net of taxes (in usd per share)		0	0
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	0.30	0.46
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution (in usd per share)		0.30	0.45
Income (loss) from discontinued operations, net of taxes - assuming dilution (in usd per share)		0	0
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	$ 0.30	$ 0.45

[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.