Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 217	$ 186	$ 691	$ 653
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $33, ($20), $35, and $14	54	(33)	58	24
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $28, ($6), $37, and ($3)	48	(8)	63	(4)
Foreign currency translation adjustments, net of income taxes of ($3), ($3), ($11), and ($3)	(5)	(9)	(18)	(12)
Net pension and postretirement benefit costs, net of income taxes of ($15), $10, ($12), and $13	(24)	14	(19)	19
Total other comprehensive income (loss), net of tax	73	(36)	84	27
Comprehensive income (loss)	290	150	775	680
Less: Comprehensive income attributable to noncontrolling interests	(2)		1	6
Comprehensive income (loss) attributable to Key	$ 292	$ 150	$ 774	$ 674