Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 542	$ 645	$ 1,523	$ 1,996
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $510, $56, $1,381, and $195	(1,616)	(174)	(4,380)	(617)
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $150, $9, $409, and $57	(477)	(29)	(1,298)	(180)
Net pension and postretirement benefit costs, net of income taxes of $0, $(3), $(2), and $(5)	2	8	7	14
Total other comprehensive income (loss), net of tax	(2,091)	(195)	(5,671)	(783)
Comprehensive income (loss)	(1,549)	450	(4,148)	1,213
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income (loss) attributable to Key	$ (1,549)	$ 450	$ (4,148)	$ 1,213