Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) SecurityLoan	Sep. 30, 2016 USD ($) SecurityLoan	Sep. 30, 2017 USD ($) SecurityLoan	Sep. 30, 2016 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	12,184	12,632	37,040	34,371
Pre-Modification Outstanding Loan Balance	$ 319	$ 873	$ 1,254	$ 1,975
Post-Modification Outstanding Loan Balance	$ 300	$ 839	$ 1,190	$ 1,849
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	616	638	2,117	1,734
Pre-Modification Outstanding Loan Balance	$ 40	$ 200	$ 239	$ 692
Post-Modification Outstanding Loan Balance	$ 27	$ 169	$ 195	$ 567
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	29	26	93	70
Pre-Modification Outstanding Loan Balance	$ 18	$ 225	$ 56	$ 242
Post-Modification Outstanding Loan Balance	$ 16	$ 223	$ 55	$ 240
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	141	700	641	1,192
Pre-Modification Outstanding Loan Balance	$ 15	$ 81	$ 72	$ 129
Post-Modification Outstanding Loan Balance	$ 16	$ 87	$ 73	$ 136
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,949	593	3,210	1,669
Pre-Modification Outstanding Loan Balance	$ 39	$ 9	$ 65	$ 27
Post-Modification Outstanding Loan Balance	$ 32	$ 9	$ 55	$ 28
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	8,106	8,051	25,657	22,693
Pre-Modification Outstanding Loan Balance	$ 38	$ 38	$ 123	$ 109
Post-Modification Outstanding Loan Balance	$ 38	$ 40	$ 124	$ 111
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	10,841	10,008	31,718	27,358
Pre-Modification Outstanding Loan Balance	$ 150	$ 553	$ 555	$ 1,199
Post-Modification Outstanding Loan Balance	$ 129	$ 528	$ 502	$ 1,082
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3	15	10	35
Pre-Modification Outstanding Loan Balance		$ 3	$ 2	$ 6
Post-Modification Outstanding Loan Balance		$ 3	$ 2	$ 6
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,340	2,609	5,312	6,978
Pre-Modification Outstanding Loan Balance	$ 169	$ 317	$ 697	$ 770
Post-Modification Outstanding Loan Balance	$ 171	$ 308	$ 686	$ 761