Acquisitions and Discontinued Operations - Additional Information (Detail) (USD $)	6 Months Ended			3 Months Ended				6 Months Ended													3 Months Ended	6 Months Ended					3 Months Ended	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Sep. 30, 2012 New York [Member]	Sep. 14, 2012 New York [Member]	Jul. 13, 2012 New York [Member] Branch	Aug. 01, 2012 Key-Branded Credit Card [Member]	Jun. 30, 2013 Portfolio Loans [Member] TDRs	Jun. 30, 2013 Carrying Amount [Member]	Dec. 31, 2012 Carrying Amount [Member]	Jun. 30, 2012 Carrying Amount [Member]	Jun. 30, 2013 Mortgage Servicing Rights [Member]	Jun. 30, 2013 Segment, Discontinued Operations [Member]	Dec. 31, 2012 Segment, Discontinued Operations [Member]	Jun. 30, 2012 Segment, Discontinued Operations [Member]	Dec. 31, 2009 Segment, Discontinued Operations [Member] Trust	Jun. 30, 2013 Segment, Discontinued Operations [Member] Carrying Amount [Member]	Jun. 30, 2012 Segment, Discontinued Operations [Member] Carrying Amount [Member]	Jun. 30, 2013 Segment, Discontinued Operations [Member] Contractual Values [Member]	Jun. 30, 2013 Segment, Discontinued Operations [Member] Fair Value [Member]	Mar. 31, 2013 Maximum [Member]	Jun. 30, 2013 Maximum [Member]	Jun. 30, 2013 Maximum [Member] Segment, Discontinued Operations [Member] Carrying Amount [Member]	Jun. 30, 2012 Maximum [Member] Segment, Discontinued Operations [Member] Carrying Amount [Member]	Jun. 30, 2013 Maximum [Member] Segment, Discontinued Operations [Member] Contractual Values [Member]	Jun. 30, 2013 Maximum [Member] Segment, Discontinued Operations [Member] Fair Value [Member]	Mar. 31, 2013 Minimum [Member]	Jun. 30, 2013 Minimum [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value of mortgage servicing rights												$ 117,000,000
Acquired credit card assets					68,000,000		718,000,000
Estimated purchased credit card relationship intangible asset					1,000,000		135,000,000
Assumed reward liability					1,000,000		9,000,000
Number of retail banking branches acquired						37
Estimated fair value of the assets and deposits acquired				2,000,000,000
Loans purchased associated with branches acquired				244,000,000
Credit impaired loans purchased associated with branches acquired				25,000,000
Business acquisition premises and equipment				8,000,000
Deposits assumed associated with branches acquired in purchase and assumption agreement				2,000,000,000
Business acquisition cash received				1,800,000,000
Business acquisition intangible asset				40,000,000
Business acquisition goodwill asset				62,000,000
Business acquisition, cash payment					68,000,000
Investment recorded								8,000,000
Allowance for loan held as investment	876,000,000	888,000,000	888,000,000					2,000,000					41,000,000	55,000,000	79,000,000
Number of TDRs								734
Number of outstanding securitization trusts																10
Economic interest or risk of loss associated with Education loan securitization trusts													202,000,000
Loans purchased	145,000,000
Loans at fair value	151,000,000	157,000,000	73,000,000						52,405,000,000	51,934,000,000	48,717,000,000
Loans held by trusts with unpaid balances ninety days or more past due																			29,000,000	30,000,000
Loans held by portfolio with unpaid balances ninety days or more past due																			4,000,000	4,000,000			35,000,000	43,000,000
Loans held by the trusts with unpaid principal balances due date													90 days or more
Loans held by the portfolio with unpaid principal balances due date													90 days or more
Loans held by the trust in nonaccrual status																			13,000,000	13,000,000
Loans held by portfolio in nonaccrual status																	6,000,000	2,000,000							1,000,000	1,000,000
After tax gain on sale of subsidiary																					155,000,000	115,000,000					145,000,000	100,000,000
Cash portion in gain																						$ 90,000,000						$ 75,000,000