Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013 M	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans pledged at the Federal Home Loan Bank ("FHLB")	$ 75,100,000,000	$ 74,100,000,000
Loans pledged at the Federal Reserve Bank	49,500,000,000	48,600,000,000
Unearned interest and deferred fees and costs on loans	667,000,000	753,000,000
Period for capturing full economic cycle in evaluation	12 years
Impairment loan threshold for allowance in which loans are individually analyzed	5,000,000
Maximum restructuring period under credit card loan financial difficulty modifications	60
Maximum restructuring period under credit card loan temporary financial hardship modifications	Up to 12 months
Outstanding balance of loans where trial period was unsuccessful and no longer eligible for a permanent modification	16,000,000
Purchased impaired loans nonperforming assets	22,000,000	82,000,000
Residential mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	94
Outstanding balance of loans in trial period	15,000,000
Estimated post-modification balance of loans in trial period	15,000,000
Home Equity and Second Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	18
Outstanding balance of loans in trial period	2,000,000
Estimated post-modification balance of loans in trial period	2,000,000
Loans purchased from GNMA mortgage pools [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	338
Outstanding balance of loans in trial period	51,000,000
Estimated post-modification balance of loans in trial period	$ 51,000,000
Government National Mortgage Association [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of residential mortgage loans, home equity and second mortgage loans, and GNMA loans where trial period arrangement was unsuccessful	97