Loans and Allowance for Credit Losses (Details Textual) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Loans and Allowance for Credit Losses (Textual) [Abstract]
Loans pledged at the Federal Home Loan Bank ("FHLB")	$ 66,500,000,000		$ 67,000,000,000
Loans pledged at the Federal Reserve Bank	48,100,000,000		47,200,000,000
Unearned interest and deferred fees and costs on loans	1,000,000,000		1,100,000,000
Purchased impaired loans nonperforming assets	100,000,000		200,000,000
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 of accruing loans related nonperforming assets and related ratios			90 days
Extension included in Commercial Real Estate Modifications	upto 12 Months
Partial charge off period of loans secured by 1-4 family properties	180 days
Charge off period of revolving consumer lines and credit cards	180 days
Charge off period of closed-end consumer loans, other than loans secured by 1-4 family properties	120 days
Net gains on the sale of loan	287,000,000	215,000,000
Minimum amount of loans for which allowance recorded for impaired purposes.	5,000,000
Period for capturing full economic cycle in evaluation	11 years
Outstanding Balance of Loans on Completion of Trial Period	141,000,000
Loans purchased from GNMA [Member]
Additional loans and allowance for credit losses (Textual) [Abstract]
Number of loans in trial period	1,104
Outstanding balance of loans in trial period	139,000,000
Estimated post-modification balance of loans in trial period	147,000,000
Residential Mortgage [Member]
Additional loans and allowance for credit losses (Textual) [Abstract]
Number of loans in trial period	325
Outstanding balance of loans in trial period	57,000,000
Estimated post-modification balance of loans in trial period	59,000,000
Government National Mortgage Association [Member]
Additional loans and allowance for credit losses (Textual) [Abstract]
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	403,000,000		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	2,700,000,000		2,600,000,000
Number of residential mortgage loans	995
Government National Mortgage Association [Member] | Trouble Debt Restructure [Member]
Additional loans and allowance for credit losses (Textual) [Abstract]
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 with a pass rating	2,700,000,000		2,600,000,000
Restructured GNMA loans that are classified with a pass rating	2,000,000,000		2,000,000,000
Other Retail [Member]
Additional loans and allowance for credit losses (Textual) [Abstract]
Number of loans in trial period	32
Outstanding balance of loans in trial period	2,000,000
Estimated post-modification balance of loans in trial period	$ 1,000,000