Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
EARNINGS
Income (loss) from continuing operations	$ 202		$ 201
Less: Net income (loss) attributable to noncontrolling interests	1
Income (loss) from continuing operations attributable to Key	201		201
Income (loss) from continuing operations attributable to Key common shareholders	196		195
Income (loss) from discontinued operations, net of taxes	3		(1)
Net income (loss) attributable to Key common shareholders	199		194
WEIGHTED-AVERAGE COMMON SHARES
Weighted-average common shares outstanding	920,316		949,342
Effect of dilutive convertible preferred stock, common share options and other stock awards	5,735		4,629
Weighted-average common shares and potential common shares outstanding	926,051	[1]	953,971	[1]
EARNINGS PER COMMON SHARE
Income (loss) from continuing operations attributable to Key common shareholders	$ 0.21		$ 0.21
Income (loss) from discontinued operations, net of taxes
Net income (loss) attributable to Key common shareholders	$ 0.22	[2]	$ 0.20	[2]
Income (loss) from continuing operations attributable to Key common shareholders - assuming dilution	$ 0.21		$ 0.20
Income (loss) from discontinued operations, net of taxes
Net income (loss) attributable to Key common shareholders - assuming dilution	$ 0.21	[2]	$ 0.20	[2]
Series A Preferred Stock [Member]
EARNINGS
Less: Dividends on Series A Preferred Stock	$ 5		$ 6

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

[2] EPS may not foot due to rounding.