Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 790	$ 920	$ 907
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of ($76), ($32), and $35	(127)	(54)	59
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of ($19), $17, and $2	(34)	28	3
Foreign currency translation adjustments, net of income taxes of ($1), ($14), and ($8)	(1)	(24)	(20)
Net pension and postretirement benefit costs, net of income taxes of $19, ($2), and ($27)	26	1	(46)
Total other comprehensive income (loss), net of tax	(136)	(49)	(4)
Comprehensive income (loss)	654	871	903
Less: Comprehensive income attributable to noncontrolling interests	(1)	4	7
Comprehensive income (loss) attributable to Key	$ 655	$ 867	$ 896