Loans and Allowance for Credit Losses - Carrying Amount of Covered Assets (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Covered Assets [Line Items]
Purchased Impaired Loans	$ 4,299	$ 5,301
Purchased Nonimpaired Loans	3,757	4,727
Other Assets	2,116	1,477
Covered loans	9,985	11,308
Total covered assets	10,172	11,505
Commercial [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Nonimpaired Loans	124	143
Other Assets
Covered loans	124	143
Commercial Real Estate [Member]
Covered Assets [Line Items]
Purchased Impaired Loans	1,095	1,323
Purchased Nonimpaired Loans	1,915	2,695
Other Assets
Covered loans	3,010	4,018
Residential Mortgages [Member]
Covered Assets [Line Items]
Purchased Impaired Loans	3,204	3,978
Purchased Nonimpaired Loans	995	1,109
Other Assets
Covered loans	4,199	5,087
Credit Card [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Nonimpaired Loans	5	5
Other Assets
Covered loans	5	5
Other Retail [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Nonimpaired Loans	718	775
Other Assets
Covered loans	718	775
Losses Reimbursable by FDIC [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Nonimpaired Loans
Other Assets	1,185	1,280
Covered loans	1,185	1,280
Unamortized Changes in FDIC asset [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Nonimpaired Loans
Other Assets	744
Covered loans	744
Covered Loans [Member]
Covered Assets [Line Items]
Purchased Impaired Loans	4,299	5,301
Purchased Nonimpaired Loans	3,757	4,727
Other Assets	1,929	1,280
Covered loans	9,985	11,308
Foreclosed Real Estate [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Nonimpaired Loans
Other Assets	187	197
Total covered assets	$ 187	$ 197