Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended					3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2009 Key Corporate Bank [Member]	Dec. 31, 2012 Key Corporate Bank [Member]	Dec. 31, 2011 Key Corporate Bank [Member]	Dec. 31, 2012 New York [Member]	Dec. 31, 2012 New York [Member] Core deposit intangibles [Member]	Dec. 31, 2012 New York [Member] Purchased Credit Card Relationship Intangible [Member]	Dec. 31, 2012 Elan Financial Services Inc[Member] Purchased Credit Card Relationship Intangible [Member]
Goodwill And Other Intangible Asset [Line Items]
Estimated fair value of the Community Bank unit greater than certain percent of carrying value				10.00%	11.00%
Pre-tax impairment charge based on additional Impairment testing						$ 223
Business acquisition, goodwill	62								62
Expected deductible goodwill for tax purpose	150
Accumulated impairment losses	665	665	665
Intangible asset										40	1	135
Useful life of intangible asset										7 years	8 years	8 years
Write off of intangible assets related to customer relationship			15
Intangible asset amortization expense	23	4	14
Estimated Amortization expense 2013	44
Estimated Amortization expense 2014	37
Estimated Amortization expense 2015	31
Estimated Amortization expense 2016	24
Estimated Amortization expense 2017	$ 18