Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 204	$ 241	$ 409	$ 441
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on securities available for sale, net of income taxes of ($74), ($25), ($87) and ($31)	(125)	(42)	(147)	(53)
Net unrealized gains (losses) on derivative financial instruments, net of income taxes of ($18), ($2), ($23) and $5	(31)	(4)	(39)	8
Foreign currency translation adjustments, net of income taxes	(3)	(10)	(14)	(4)
Net pension and postretirement benefit costs, net of income taxes	3	3	6	5
Total other comprehensive income (loss), net of tax	(156)	(53)	(194)	(44)
Comprehensive income (loss)	48	188	215	397
Less: Comprehensive income attributable to noncontrolling interests		5	1	5
Comprehensive income (loss) attributable to Key	$ 48	$ 183	$ 214	$ 392