Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) SecurityLoan	Jun. 30, 2016 USD ($) SecurityLoan	Jun. 30, 2017 USD ($) SecurityLoan	Jun. 30, 2016 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	10,687	9,368	24,856	21,739
Pre-Modification Outstanding Loan Balance	$ 305	$ 541	$ 935	$ 1,102
Post-Modification Outstanding Loan Balance	$ 279	$ 449	$ 890	$ 1,010
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	671	495	1,501	1,096
Pre-Modification Outstanding Loan Balance	$ 62	$ 332	$ 199	$ 492
Post-Modification Outstanding Loan Balance	$ 40	$ 237	$ 168	$ 398
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	41	20	64	44
Pre-Modification Outstanding Loan Balance	$ 29	$ 10	$ 38	$ 17
Post-Modification Outstanding Loan Balance	$ 31	$ 10	$ 39	$ 17
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	144	214	500	492
Pre-Modification Outstanding Loan Balance	$ 17	$ 16	$ 57	$ 48
Post-Modification Outstanding Loan Balance	$ 16	$ 17	$ 57	$ 49
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	639	467	1,261	1,076
Pre-Modification Outstanding Loan Balance	$ 15	$ 7	$ 26	$ 18
Post-Modification Outstanding Loan Balance	$ 14	$ 8	$ 23	$ 19
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	8,146	6,654	17,551	14,642
Pre-Modification Outstanding Loan Balance	$ 40	$ 33	$ 85	$ 71
Post-Modification Outstanding Loan Balance	$ 40	$ 32	$ 86	$ 71
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	9,641	7,850	20,877	17,350
Pre-Modification Outstanding Loan Balance	$ 163	$ 398	$ 405	$ 646
Post-Modification Outstanding Loan Balance	$ 141	$ 304	$ 373	$ 554
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3	17	7	20
Pre-Modification Outstanding Loan Balance	$ 1	$ 3	$ 2	$ 3
Post-Modification Outstanding Loan Balance	$ 1	$ 3	$ 2	$ 3
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,043	1,501	3,972	4,369
Pre-Modification Outstanding Loan Balance	$ 141	$ 140	$ 528	$ 453
Post-Modification Outstanding Loan Balance	$ 137	$ 142	$ 515	$ 453