Acquisition and Discontinued Operations - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Western New York Branches [Member]	Sep. 30, 2012 Western New York Branches [Member]	Sep. 14, 2012 Western New York Branches [Member]	Jul. 13, 2012 Western New York Branches [Member] Branch	Sep. 30, 2012 Key-Branded Credit Card [Member]	Aug. 01, 2012 Key-Branded Credit Card [Member]	Sep. 30, 2012 Portfolio Loans [Member] TDRs	Sep. 30, 2012 Portfolio Loans [Member] Maximum [Member]	Sep. 30, 2012 Retained Earnings [Member]	Dec. 31, 2011 Retained Earnings [Member]	Sep. 30, 2011 Retained Earnings [Member]	Dec. 31, 2010 Retained Earnings [Member]	Jan. 01, 2010 Retained Earnings [Member]	Sep. 30, 2012 Segment, Discontinued Operations [Member]	Dec. 31, 2011 Segment, Discontinued Operations [Member]	Sep. 30, 2011 Segment, Discontinued Operations [Member]	Jan. 01, 2010 Segment, Discontinued Operations [Member] Trust	Sep. 30, 2012 Segment, Discontinued Operations [Member] Contractual Values [Member]	Sep. 30, 2012 Segment, Discontinued Operations [Member] Contractual Values [Member] Maximum [Member]	Sep. 30, 2012 Segment, Discontinued Operations [Member] Fair Value [Member]	Sep. 30, 2012 Segment, Discontinued Operations [Member] Fair Value [Member] Maximum [Member]	Sep. 30, 2012 Segment, Discontinued Operations [Member] Carrying Value Amount [Member]	Dec. 31, 2011 Segment, Discontinued Operations [Member] Carrying Value Amount [Member]	Sep. 30, 2011 Segment, Discontinued Operations [Member] Carrying Value Amount [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of retail banking branches acquired							37
Estimated fair value of the assets and deposits acquired				$ 2,000,000,000	$ 2,000,000,000
Loans purchased associated with branches acquired				244,000,000	244,000,000
Credit impaired loans purchased associated with branches acquired				25,000,000	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	2,000,000,000
Business acquisition cash received				1,800,000,000
Business acquisition Intangible asset				40,000,000	40,000,000
Business acquisition goodwill asset				62,000,000	62,000,000
Increase in allowance for loan and lease losses		243,000,000			5,000,000			24,000,000
Amortization expense related to intangible asset					2,000,000			6,000,000
Acquired Credit card assets						69,000,000			718,000,000
Assumed reward liability						1,000,000			9,000,000
Business acquisition, cash payment						68,000,000
Estimated purchased credit card relationship intangible asset									135,000,000
Investment recorded										3,000,000
Allowance for loan held as investment	1,131,000,000	888,000,000	1,004,000,000								1,000,000						65,000,000	104,000,000	115,000,000
Number of TDRs										246
Number of outstanding securitization trusts																				10
Economic interest or risk of loss associated with Education loan securitization trusts																	207,000,000
Cumulative effect adjustment to beginning balance of Retained Earnings	9,918,000,000	10,279,000,000	9,922,000,000									6,762,000,000	6,246,000,000	6,079,000,000	5,557,000,000	45,000,000
Overstate accrued income and other assets	30,000,000
Loans held by trusts with unpaid balances ninety days or more past due																					38,000,000		36,000,000
Loans held by portfolio with unpaid balances ninety days or more past due																					2,000,000		3,000,000		47,000,000	48,000,000	49,000,000
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																					16,000,000		15,000,000
Loans held by portfolio in nonaccrual status																						$ 1,000,000		$ 1,000,000	$ 5,000,000	$ 3,000,000	$ 3,000,000