Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans pledged at the Federal Home Loan Bank ("FHLB")	$ 75,300,000,000	$ 75,300,000,000	$ 74,100,000,000
Loans pledged at the Federal Reserve Bank	51,600,000,000	51,600,000,000	48,600,000,000
Unearned interest and deferred fees and costs on loans	539,000,000	539,000,000	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 months
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	18,000,000	59,000,000
Purchased impaired loans included in covered loans classified as nonperforming assets	9,000,000	9,000,000	82,000,000
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	142	142
Outstanding balance of loans in trial period	18,000,000	18,000,000
Estimated post-modification balance of loans in trial period	16,000,000	16,000,000
Home Equity and Second Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of loans in trial period	5	5
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	1,905	1,905
Outstanding balance of loans in trial period	247,000,000	247,000,000
Estimated post-modification balance of loans in trial period	$ 231,000,000	$ 231,000,000
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	135	441