Loans and Allowance for Credit Losses - Carrying Amount of Covered Assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Covered Assets [Line Items]
Purchased Impaired Loans	$ 4,452	$ 5,301
Purchased Non-impaired Loans	4,136	4,727
Other Assets	2,315	1,477
Total	10,903	11,505
Commercial [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Non-impaired Loans	126	143
Other Assets
Total	126	143
Commercial Real Estate [Member]
Covered Assets [Line Items]
Purchased Impaired Loans	1,214	1,323
Purchased Non-impaired Loans	2,206	2,695
Other Assets
Total	3,420	4,018
Residential Mortgages [Member]
Covered Assets [Line Items]
Purchased Impaired Loans	3,238	3,978
Purchased Non-impaired Loans	1,055	1,109
Other Assets
Total	4,293	5,087
Credit Card [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Non-impaired Loans	5	5
Other Assets
Total	5	5
Other Retail [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Non-impaired Loans	744	775
Other Assets
Total	744	775
Losses reimbursable by FDIC [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Non-impaired Loans
Other Assets	1,298	1,280
Total	1,298	1,280
Unamortized Changes in FDIC asset [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Non-impaired Loans
Other Assets	849
Total	849
Covered Loans [Member]
Covered Assets [Line Items]
Purchased Impaired Loans	4,452	5,301
Purchased Non-impaired Loans	4,136	4,727
Other Assets	2,147	1,280
Total	10,735	11,308
Foreclosed real estate [Member]
Covered Assets [Line Items]
Purchased Impaired Loans
Purchased Non-impaired Loans
Other Assets	168	197
Total	$ 168	$ 197