Condensed Financial Information of the Parent Company (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING ACTIVITIES
Net income (loss) attributable to Key	$ 920	$ 554	$ (1,335)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Gain related to exchange of common shares for capital securities			(78)
Deferred income taxes (benefit)	(310)	80	(878)
Other operating activities, net	996	509	995
NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES	1,890	2,724	2,320
INVESTING ACTIVITIES
Purchases of securities available for sale	(624)	(9,914)	(15,501)
Proceeds from prepayments and maturities of securities available for sale	5,000	4,685	4,275
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	1,642	1,974	6,609
FINANCING ACTIVITIES
Net increase (decrease) in short-term borrowings	(1,148)	1,114	(7,952)
Net proceeds from issuance of long-term debt	1,031	797	763
Payments on long-term debt	(2,215)	(1,657)	(3,726)
Net proceeds from issuance of common shares and preferred stock	604		986
Cash dividends paid	(164)	(184)	(213)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	(3,116)	(4,891)	(9,703)
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	416	(193)	(774)
CASH AND DUE FROM BANKS AT BEGINNING OF YEAR	278	471	1,245
CASH AND DUE FROM BANKS AT END OF YEAR	694	278	471
Condensed Financial Information of Parent Company (Textual) [Abstract]
Interest Paid	151	131	167
Parent Company [Member]
OPERATING ACTIVITIES
Net income (loss) attributable to Key	920	554	(1,335)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Gain related to exchange of common shares for capital securities			(78)
Deferred income taxes (benefit)	(39)	(23)	11
Income (Loss) from Equity Method Investments	749	632	(1,237)
Net increase in other assets	(130)	(186)	(96)
Net increase (decrease) in other liabilities	(43)	(27)	(274)
Other operating activities, net	83	93	157
NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES	42	(221)	(378)
INVESTING ACTIVITIES
Net (increase) decrease in interest-bearing deposits	3,207	163	1,303
Purchases of securities available for sale	(18)	(31)	(18)
Proceeds from prepayments and maturities of securities available for sale	32	32	20
Net decrease in loans and advances to subsidiaries	939	170	69
Net (Increase) decrease in investments in subsidiaries	2	(77)	(1,200)
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	4,162	257	174
FINANCING ACTIVITIES
Net proceeds from issuance of long-term debt	1,000	750	436
Payments on long-term debt	(1,043)	(602)	(1,000)
Series B Preferred Stock - TARP redemption	(2,500)
Net proceeds from issuance of common shares and preferred stock	604		986
Net proceeds from the issuance of common stock warrant	(70)
Cash dividends paid	(164)	(184)	(213)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	(2,173)	(36)	204
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	2,031
CASH AND DUE FROM BANKS AT BEGINNING OF YEAR	0	0	0
CASH AND DUE FROM BANKS AT END OF YEAR	$ 2,031	$ 0	$ 0