Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2016 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	12,632	10,766	34,371	31,004
Pre-Modification Outstanding Loan Balance	$ 873	$ 482	$ 1,975	$ 1,403
Post-Modification Outstanding Loan Balance	$ 839	$ 473	$ 1,849	$ 1,395
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	638	381	1,734	1,170
Pre-Modification Outstanding Loan Balance	$ 200	$ 111	$ 692	$ 227
Post-Modification Outstanding Loan Balance	$ 169	$ 102	$ 567	$ 223
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	26	35	70	89
Pre-Modification Outstanding Loan Balance	$ 225	$ 24	$ 242	$ 64
Post-Modification Outstanding Loan Balance	$ 223	$ 23	$ 240	$ 62
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	700	381	1,192	1,820
Pre-Modification Outstanding Loan Balance	$ 81	$ 48	$ 129	$ 234
Post-Modification Outstanding Loan Balance	$ 87	$ 47	$ 136	$ 232
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	593	690	1,669	1,974
Pre-Modification Outstanding Loan Balance	$ 9	$ 19	$ 27	$ 42
Post-Modification Outstanding Loan Balance	$ 9	$ 19	$ 28	$ 42
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	8,051	7,289	22,693	19,978
Pre-Modification Outstanding Loan Balance	$ 38	$ 35	$ 109	$ 100
Post-Modification Outstanding Loan Balance	$ 40	$ 36	$ 111	$ 101
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	10,008	8,776	27,358	25,031
Pre-Modification Outstanding Loan Balance	$ 553	$ 237	$ 1,199	$ 667
Post-Modification Outstanding Loan Balance	$ 528	$ 227	$ 1,082	$ 660
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	15	4	35	13
Pre-Modification Outstanding Loan Balance	$ 3	$ 1	$ 6	$ 4
Post-Modification Outstanding Loan Balance	$ 3	$ 1	$ 6	$ 4
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,609	1,986	6,978	5,960
Pre-Modification Outstanding Loan Balance	$ 317	$ 244	$ 770	$ 732
Post-Modification Outstanding Loan Balance	$ 308	$ 245	$ 761	$ 731