Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
EARNINGS
Income (loss) from continuing operations		$ 540	$ 643	$ 1,517	$ 1,985
Less: Net income (loss) attributable to noncontrolling interests		0	0	0	0
Income (loss) from continuing operations attributable to Key		540	643	1,517	1,985
Less: Dividends on Preferred Stock		27	27	80	80
Income (loss) from continuing operations attributable to Key common shareholders		513	616	1,437	1,905
Income (loss) from discontinued operations, net of taxes		2	2	6	11
Net income (loss) attributable to Key common shareholders		$ 515	$ 618	$ 1,443	$ 1,916
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average common shares outstanding (in shares)		924,594	942,446	924,085	955,069
Effect of common share options and other stock awards (in shares)		7,861	10,077	8,679	9,712
Weighted-average Common Shares and potential Common Shares outstanding (in shares)	[1]	932,455	952,523	932,764	964,781
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders (in usd per share)		$ 0.55	$ 0.65	$ 1.55	$ 1.99
Income (loss) from discontinued operations, net of taxes (in usd per share)		0	0	0.01	0.01
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	0.55	0.66	1.56	2.00
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution (in usd per share)		0.55	0.65	1.54	1.98
Income (loss) from discontinued operations, net of taxes - assuming dilution (in usd per share)		0	0	0.01	0.01
Net income (loss) attributable to Key common shareholders (in usd per share)	[2]	$ 0.55	$ 0.65	$ 1.55	$ 1.99

[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.