Earnings Per Common Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
EARNINGS
Income (loss) from continuing operations	$ 231		$ 252		$ 436		$ 534
Less: Net income (loss) attributable to noncontrolling interests	5		3		5		11
Income (loss) from continuing operations attributable to Key	226		249		431		523
Income (loss) from continuing operations attributable to Key common shareholders	221		243		420		427
Income (loss) from discontinued operations, net of taxes	10		(9)		5		(20)
Net income (loss) attributable to Key common shareholders	231		234		425		407
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average common shares outstanding (000)	944,648	[1]	947,565	[1]	946,995	[1]	914,911	[1]
Effect of dilutive convertible preferred stock, common stock options and other stock awards (000)	3,439		4,568		4,034		5,251
Weighted-average common shares and potential common shares outstanding (000)	948,087		952,133		951,029		920,162
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders	$ 0.23		$ 0.26		$ 0.44		$ 0.47
Income (loss) from discontinued operations, net of taxes	$ 0.01		$ (0.01)		$ 0.01		$ (0.02)
Net income (loss) attributable to Key common shareholders	$ 0.24		$ 0.25		$ 0.45		$ 0.44
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution	$ 0.23		$ 0.26		$ 0.44		$ 0.46
Income (loss) from discontinued operations, net of taxes	$ 0.01		$ (0.01)		$ 0.01		$ (0.02)
Net income (loss) attributable to Key common shareholders - assuming dilution	$ 0.24	[2]	$ 0.25	[2]	$ 0.45	[2]	$ 0.44	[2]
Series A Preferred Stock [Member]
EARNINGS
Less: Dividends on Series A Preferred Stock	5		6		11		12
Series B Preferred Stock [Member]
EARNINGS
Less: Dividends on Series A Preferred Stock							31
Amortization of discount on Series B Preferred Stock							$ 53

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

[2] EPS may not foot due to rounding.