Condensed Financial Information of the Parent Company - Condensed Statements of Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Other income	[1]	$ 147	$ 15	$ 68
Total interest income		4,367	4,685	5,235
Interest on long-term debt with subsidiary trusts		221	286	454
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries		3,281	1,585	2,054
Income tax (expense) benefit		(642)	(227)	(314)
NET INCOME (LOSS)		2,625	1,343	1,717
Less: Net income attributable to noncontrolling interests		0	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO KEY		2,625	1,343	1,717
Key
Condensed Financial Statements, Captions [Line Items]
Interest income from subsidiaries		1	4	9
Other income		36	8	11
Total interest income		2,012	1,262	1,294
Interest on long-term debt with subsidiary trusts		13	18	22
Interest on other borrowed funds		65	114	151
Personnel and other expense		101	63	87
Total expense		179	195	260
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries		1,833	1,067	1,034
Income tax (expense) benefit		38	38	57
Income (loss) before equity in net income (loss) less dividends from subsidiaries		1,871	1,105	1,091
Equity in net income (loss) less dividends from subsidiaries		754	238	626
NET INCOME (LOSS)		2,625	1,343	1,717
Less: Net income attributable to noncontrolling interests		0	0	0
NET INCOME (LOSS) ATTRIBUTABLE TO KEY		2,625	1,343	1,717
Key | Banks
Condensed Financial Statements, Captions [Line Items]
Bank/Nonbank subsidiaries		1,925	1,250	1,204
Key | Nonbank subsidiaries
Condensed Financial Statements, Captions [Line Items]
Bank/Nonbank subsidiaries		$ 50	$ 0	$ 70

[1] Net securities gains (losses) totaled $7 million for the year ended December 31, 2021, $4 million for the year ended December 31, 2020, and $20 million for the year ended December 31, 2019. For 2021, 2020, and 2019, we did not have any impairment losses related to securities.