Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 312	$ 448
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $(181) and $562	575	(1,784)
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $(77) and $177	245	(561)
Net pension and postretirement benefit costs, net of income taxes of $0 and $(1)	1	2
Total other comprehensive income (loss), net of tax	821	(2,343)
Comprehensive income (loss)	1,133	(1,895)
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to Key	$ 1,133	$ (1,895)