Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019 USD ($) SecurityLoan	Jun. 30, 2018 USD ($) SecurityLoan	Jun. 30, 2019 USD ($) SecurityLoan	Jun. 30, 2018 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	11,090	11,103	23,878	21,896
Pre-Modification Outstanding Loan Balance	$ 399	$ 519	$ 760	$ 804
Post-Modification Outstanding Loan Balance	$ 388	$ 510	$ 732	$ 783
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	823	724	1,736	1,347
Pre-Modification Outstanding Loan Balance	$ 90	$ 132	$ 126	$ 213
Post-Modification Outstanding Loan Balance	$ 86	$ 126	$ 115	$ 201
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	24	30	44	59
Pre-Modification Outstanding Loan Balance	$ 25	$ 15	$ 72	$ 31
Post-Modification Outstanding Loan Balance	$ 24	$ 14	$ 70	$ 30
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	105	105	201	253
Pre-Modification Outstanding Loan Balance	$ 12	$ 20	$ 26	$ 37
Post-Modification Outstanding Loan Balance	$ 13	$ 20	$ 26	$ 36
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	642	535	1,215	1,094
Pre-Modification Outstanding Loan Balance	$ 13	$ 17	$ 24	$ 28
Post-Modification Outstanding Loan Balance	$ 13	$ 17	$ 23	$ 27
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	7,941	7,461	17,589	16,007
Pre-Modification Outstanding Loan Balance	$ 44	$ 37	$ 94	$ 80
Post-Modification Outstanding Loan Balance	$ 44	$ 38	$ 95	$ 81
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	9,535	8,855	20,785	18,760
Pre-Modification Outstanding Loan Balance	$ 184	$ 221	$ 342	$ 389
Post-Modification Outstanding Loan Balance	$ 180	$ 215	$ 329	$ 375
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	1,555	2,248	3,093	3,136
Pre-Modification Outstanding Loan Balance	$ 215	$ 298	$ 418	$ 415
Post-Modification Outstanding Loan Balance	$ 208	$ 295	$ 403	$ 408

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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