Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($) SecurityLoan	Jun. 30, 2019 USD ($) SecurityLoan	Jun. 30, 2020 USD ($) SecurityLoan	Jun. 30, 2019 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	8,849	11,090	20,939	23,878
Pre-Modification Outstanding Loan Balance	$ 395	$ 399	$ 852	$ 760
Post-Modification Outstanding Loan Balance	$ 362	$ 388	$ 815	$ 732
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	1,139	823	2,138	1,736
Pre-Modification Outstanding Loan Balance	$ 144	$ 90	$ 243	$ 126
Post-Modification Outstanding Loan Balance	$ 115	$ 86	$ 216	$ 115
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	38	24	65	44
Pre-Modification Outstanding Loan Balance	$ 39	$ 25	$ 60	$ 72
Post-Modification Outstanding Loan Balance	$ 39	$ 24	$ 60	$ 70
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	121	105	211	201
Pre-Modification Outstanding Loan Balance	$ 24	$ 12	$ 34	$ 26
Post-Modification Outstanding Loan Balance	$ 24	$ 13	$ 34	$ 26
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	374	642	1,029	1,215
Pre-Modification Outstanding Loan Balance	$ 9	$ 13	$ 24	$ 24
Post-Modification Outstanding Loan Balance	$ 8	$ 13	$ 22	$ 23
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	6,168	7,941	14,583	17,589
Pre-Modification Outstanding Loan Balance	$ 37	$ 44	$ 83	$ 94
Post-Modification Outstanding Loan Balance	$ 38	$ 44	$ 85	$ 95
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	7,840	9,535	18,026	20,785
Pre-Modification Outstanding Loan Balance	$ 253	$ 184	$ 444	$ 342
Post-Modification Outstanding Loan Balance	$ 224	$ 180	$ 417	$ 329
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	1,009	1,555	2,913	3,093
Pre-Modification Outstanding Loan Balance	$ 142	$ 215	$ 408	$ 418
Post-Modification Outstanding Loan Balance	$ 138	$ 208	$ 398	$ 403

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

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