Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 533	$ 729	$ 981	$ 1,351
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $309, $(59), $871, and $139	(980)	185	(2,764)	(443)
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $82, $45, $259, and $48	(260)	(141)	(821)	(151)
Net pension and postretirement benefit costs, net of income taxes of $(1), $(1), $(2), and $(2)	3	3	5	6
Total other comprehensive income (loss), net of tax	(1,237)	47	(3,580)	(588)
Comprehensive income (loss)	(704)	776	(2,599)	763
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income (loss) attributable to Key	$ (704)	$ 776	$ (2,599)	$ 763