Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans pledged at the Federal Home Loan Bank ("FHLB")	$ 73,200,000,000		$ 73,200,000,000			$ 67,000,000,000
Loans pledged at the Federal Reserve Bank	47,200,000,000		47,200,000,000			47,200,000,000
Unearned interest and deferred fees and costs on loans	800,000,000		800,000,000			1,100,000,000
Fair value of impaired loans acquired in BankEast transaction					28,000,000
Receivables of impaired loans acquired in BankEast transaction					63,000,000
Cash Receivables of impaired loans acquired in BankEast transaction to be collected with interest					41,000,000
Fair value of non-impaired loans acquired in BankEast transaction					96,000,000
Receivables of Non-Impaired Loans Acquired in BankEast transaction					135,000,000
Cash Receivables of non-impaired loans acquired in BankEast transaction not expected to be collected					22,000,000
Period for capturing full economic cycle in evaluation			11 years
Minimum amount of loans for which allowance recorded for impaired purposes			5,000,000
Period of accruing loans related nonperforming assets and related ratios			90 days
Extension included in Commercial Real Estate Modifications			up to 12 Months
Outstanding balance of loans where trial period was unsuccessful and no longer eligible for a permanent modification	50,000,000
Purchased impaired loans nonperforming assets	93,000,000		93,000,000			189,000,000
Net gains on the sale of loan	419,000,000	74,000,000	998,000,000	340,000,000
Government National Mortgage Association
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 days past due purchased from Government National Mortgage Association mortgage pools whose payments are insured by the Federal Housing Administration and classified as current	462,000,000		462,000,000			545,000,000
Loans 90 days or more past due purchased from Government National Mortgage Association mortgage pools whose payments are insured by the Federal Housing Administration and classified as current	3,000,000,000		3,000,000,000			2,600,000,000
Number of residential mortgage loans, home equity and second mortgage loans, and GNMA loans where trial period arrangement was unsuccessful	309
Government National Mortgage Association | Trouble Debt Restructure
Financing Receivable, Recorded Investment, Past Due [Line Items]
Restructured GNMA loans that are classified with a pass rating	2,200,000,000		2,200,000,000			2,000,000,000
Loans 90 days or more past due purchased from Government National Mortgage Association mortgage pools whose payments are insured by the Federal Housing Administration and classified as current	3,000,000,000		3,000,000,000			2,600,000,000
Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	250		250
Outstanding balance of loans in trial period	43,000,000		43,000,000
Estimated post-modification balance of loans in trial period	44,000,000		44,000,000
Home Equity and Second Mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	29		29
Outstanding balance of loans in trial period	2,000,000		2,000,000
Estimated post-modification balance of loans in trial period	2,000,000		2,000,000
Loans purchased from GNMA
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	2,180		2,180
Outstanding balance of loans in trial period	263,000,000		263,000,000
Estimated post-modification balance of loans in trial period	$ 271,000,000		$ 271,000,000