Loans and Allowance for Credit Losses - Carrying Amount of Covered Assets (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Covered Assets [Line Items]
Covered loans	$ 9,396	$ 11,308
Total covered assets	9,572	11,505
Purchased Impaired Loans	4,076	5,301
Purchased Nonimpaired Loans	3,535	4,727
Other Assets	1,961	1,477
Commercial [Member]
Covered Assets [Line Items]
Covered loans	109	143
Purchased Impaired Loans
Purchased Nonimpaired Loans	109	143
Other Assets
Commercial Real Estate [Member]
Covered Assets [Line Items]
Covered loans	2,776	4,018
Purchased Impaired Loans	973	1,323
Purchased Nonimpaired Loans	1,803	2,695
Other Assets
Residential Mortgages [Member]
Covered Assets [Line Items]
Covered loans	4,038	5,087
Purchased Impaired Loans	3,103	3,978
Purchased Nonimpaired Loans	935	1,109
Other Assets
Credit Card [Member]
Covered Assets [Line Items]
Covered loans	5	5
Purchased Impaired Loans
Purchased Nonimpaired Loans	5	5
Other Assets
Other Retail [Member]
Covered Assets [Line Items]
Covered loans	683	775
Purchased Impaired Loans
Purchased Nonimpaired Loans	683	775
Other Assets
Losses Reimbursable by FDIC [Member]
Covered Assets [Line Items]
Covered loans	820	1,280
Purchased Impaired Loans
Purchased Nonimpaired Loans
Other Assets	820	1,280
Unamortized Changes in FDIC asset [Member]
Covered Assets [Line Items]
Covered loans	965
Purchased Impaired Loans
Purchased Nonimpaired Loans
Other Assets	965
Covered Loans [Member]
Covered Assets [Line Items]
Covered loans	9,396	11,308
Purchased Impaired Loans	4,076	5,301
Purchased Nonimpaired Loans	3,535	4,727
Other Assets	1,785	1,280
Foreclosed Real Estate [Member]
Covered Assets [Line Items]
Total covered assets	176	197
Purchased Impaired Loans
Purchased Nonimpaired Loans
Other Assets	$ 176	$ 197