Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	10,766	10,809	31,004	32,941
Pre-Modification Outstanding Loan Balance	$ 482	$ 447	$ 1,403	$ 1,439
Post-Modification Outstanding Loan Balance	$ 473	$ 444	$ 1,395	$ 1,408
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	381	448	1,170	1,633
Pre-Modification Outstanding Loan Balance	$ 111	$ 28	$ 227	$ 181
Post-Modification Outstanding Loan Balance	$ 102	$ 26	$ 223	$ 169
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	35	27	89	54
Pre-Modification Outstanding Loan Balance	$ 24	$ 14	$ 64	$ 33
Post-Modification Outstanding Loan Balance	$ 23	$ 13	$ 62	$ 28
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	381	525	1,820	1,732
Pre-Modification Outstanding Loan Balance	$ 48	$ 71	$ 234	$ 232
Post-Modification Outstanding Loan Balance	$ 47	$ 70	$ 232	$ 231
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	7,289	6,708	19,978	20,040
Pre-Modification Outstanding Loan Balance	$ 35	$ 35	$ 100	$ 111
Post-Modification Outstanding Loan Balance	$ 36	$ 36	$ 101	$ 112
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	690	810	1,974	2,246
Pre-Modification Outstanding Loan Balance	$ 19	$ 18	$ 42	$ 52
Post-Modification Outstanding Loan Balance	$ 19	$ 18	$ 42	$ 52
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	8,776	8,518	25,031	25,705
Pre-Modification Outstanding Loan Balance	$ 237	$ 166	$ 667	$ 609
Post-Modification Outstanding Loan Balance	$ 227	$ 163	$ 660	$ 592
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	4	18	13	38
Pre-Modification Outstanding Loan Balance	$ 1	$ 3	$ 4	$ 14
Post-Modification Outstanding Loan Balance	$ 1	$ 3	$ 4	$ 13
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,986	2,273	5,960	7,198
Pre-Modification Outstanding Loan Balance	$ 244	$ 278	$ 732	$ 816
Post-Modification Outstanding Loan Balance	$ 245	$ 278	$ 731	$ 803