Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended		12 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2012 Key Community Bank [Member]	Dec. 31, 2010 Key Community Bank [Member]	Mar. 31, 2009 Key Corporate Bank [Member]	Dec. 31, 2012 Key Corporate Bank [Member]	Dec. 31, 2011 Key Corporate Bank [Member]
Goodwill [Line Items]
Beginning Balance	$ 917	$ 917	$ 917	$ 917
Impairment losses based on results of interim impairment testing					223
Acquisition of Western New York branches	62		62
Ending Balance	$ 979	$ 917	$ 979	$ 917