Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 M	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans pledged at the Federal Home Loan Bank ("FHLB")	$ 74,000,000,000	$ 74,000,000,000	$ 74,100,000,000
Loans pledged at the Federal Reserve Bank	51,000,000,000	51,000,000,000	48,600,000,000
Unearned interest and deferred fees and costs on loans	605,000,000	605,000,000	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	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	25,000,000	41,000,000
Purchased impaired loans included in covered loans classified as nonperforming assets	8,000,000	8,000,000	82,000,000
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	189	189
Outstanding balance of loans in trial period	31,000,000	31,000,000
Estimated post-modification balance of loans in trial period	31,000,000	31,000,000
Home Equity and Second Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	2	2
Outstanding balance of loans in trial period	1,000,000	1,000,000
Estimated post-modification balance of loans in trial period	1,000,000	1,000,000
Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	299	299
Outstanding balance of loans in trial period	38,000,000	38,000,000
Estimated post-modification balance of loans in trial period	$ 36,000,000	$ 36,000,000
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	209	306