Earnings Per Common Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
EARNINGS
Income (loss) from continuing operations	$ 976		$ 607		$ (1,263)
Less: Net income (loss) attributable to noncontrolling interests	12		30		24
Income (loss) from continuing operations attributable to Key	964		577		(1,287)
Noncash deemed dividend - common shares exchanged for Series A Preferred Stock					114
Income (loss) from continuing operations attributable to Key common shareholders	857		413		(1,581)
Income (loss) from discontinued operations, net of taxes	(44)		(23)		(48)
Net income (loss) attributable to Key common shareholders	813		390		(1,629)
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average common shares outstanding (000)	931,934	[1]	874,748	[1]	697,155	[1]
Effect of dilutive convertible preferred stock, common stock options and other stock awards (000)	3,867		3,405
Weighted-average common shares and potential common shares outstanding (000)	935,801		878,153		697,155
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders	$ 0.92		$ 0.47		$ (2.27)
Income (loss) from discontinued operations, net of taxes	$ (0.05)		$ (0.03)		$ (0.07)
Net income (loss) attributable to Key common shareholders	$ 0.87	[2]	$ 0.45	[2]	$ (2.34)	[2]
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution	$ 0.92		$ 0.47		$ (2.27)
Income (loss) from discontinued operations, net of taxes	$ (0.05)		$ (0.03)		$ (0.07)
Net income (loss) attributable to Key common shareholders - assuming dilution	$ 0.87	[2]	$ 0.44	[2]	$ (2.34)	[2]
Series A Preferred Stock [Member]
EARNINGS
Less: Dividends on Series A Preferred Stock	23		23		39
Series B Preferred Stock [Member]
EARNINGS
Less: Dividends on Series A Preferred Stock	31		125		125
Amortization of discount on Series B Preferred Stock	$ 53		$ 16		$ 16

[1] Assumes conversion of stock options and/or Preferred Series A, as applicable.

[2] EPS may not foot due to rounding.