Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 448	$ 622
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $562 and $(198)	(1,784)	(628)
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $177 and $(3)	(561)	(10)
Net pension and postretirement benefit costs, net of income taxes of $(1) and $1	2	3
Total other comprehensive income (loss), net of tax	(2,343)	(635)
Comprehensive income (loss)	(1,895)	(13)
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to Key	$ (1,895)	$ (13)