Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 2,625	$ 1,343	$ 1,717
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $306, $(143), and $(151)	(970)	452	488
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $122, $(72), and $(93)	(388)	226	300
Foreign currency translation adjustments, net of income taxes of $0, $0, and $(4)	0	0	14
Net pension and postretirement benefit costs, net of income taxes of $(11), $(9), and $(13)	34	34	42
Total other comprehensive income (loss), net of tax	(1,324)	712	844
Comprehensive income (loss) attributable to Key	$ 1,301	$ 2,055	$ 2,561