Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 907	$ 910	$ 865
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of $35, ($173), and ($58)	59	(292)	(98)
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of $2, ($17), and $12	3	(29)	20
Foreign currency translation adjustments, net of income taxes of ($8), ($3), and ($3)	(20)	(13)	10
Net pension and postretirement benefit costs, net of income taxes of ($27), $63, and ($17)	(46)	106	(28)
Net current-period other comprehensive income, net of income taxes	(4)	(228)	(96)
Comprehensive income (loss)	903	682	769
Less: Comprehensive income attributable to noncontrolling interests	7		7
Comprehensive income (loss) attributable to Key	$ 896	$ 682	$ 762