Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 173	$ 217	$ 562	$ 691
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of ($18), $33, $93 and $35	(28)	54	159	58
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of ($24), $28, $32, and $37	(41)	48	53	63
Foreign currency translation adjustments, net of income taxes of ($1), ($3), $3, and ($11)	(2)	(5)	5	(18)
Net pension and postretirement benefit costs, net of income taxes of $1, ($15), $6, and ($12)	3	(24)	6	(19)
Total other comprehensive income (loss), net of tax	(68)	73	223	84
Comprehensive income (loss)	105	290	785	775
Less: Comprehensive income attributable to noncontrolling interests	1	(2)	0	1
Comprehensive income (loss) attributable to Key	$ 104	$ 292	$ 785	$ 774