Loans Held for Sale - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan receivable held for sale for retail branches					$ 521,000,000
Residential Mortgage Loan Receivable Held for Sale for Retail Branches					1,400,000,000
Credit card receivable held for sale for retail branches					416,000,000
Other consumer loan receivable held for sale for retail branches					161,000,000
Fair value of commercial LAF loans held for sale	424,000,000		424,000,000		377,000,000
Fair value of commercial real estate loans held for sale	19,000,000		19,000,000		55,000,000
Residential mortgage loans held for sale include subprime residential mortgage loans at fair value	94,000,000		94,000,000		181,000,000
Subprime residential mortgage loans sold			64,000,000	179,000,000
Loans held for sale	1,056,000,000		1,056,000,000		3,670,000,000
Cumulative fair value adjustment on loans held for sale	169,000,000		169,000,000		251,000,000
Loss on trading related revenue associated with this economic hedging program	4,000,000		0	8,000,000
Gain on trading related revenue associated with this economic hedging program		3,000,000	0
Student loans [Member] | Other Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	65,000,000		65,000,000		70,000,000
First Niagara [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan receivable held for sale for retail branch					2,500,000,000
Commercial loan receivable held for sale for retail branches					521,000,000
Residential Mortgage Loan Receivable Held for Sale for Retail Branches					1,400,000,000
Credit card receivable held for sale for retail branches					416,000,000
Other consumer loan receivable held for sale for retail branches					$ 161,000,000