Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) SecurityLoan	Jun. 30, 2017 USD ($) SecurityLoan	Jun. 30, 2018 USD ($) SecurityLoan	Jun. 30, 2017 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	11,103	10,687	21,896	24,856
Pre-Modification Outstanding Loan Balance	$ 519	$ 305	$ 804	$ 935
Post-Modification Outstanding Loan Balance	$ 510	$ 279	$ 783	$ 890
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	724	671	1,347	1,501
Pre-Modification Outstanding Loan Balance	$ 132	$ 62	$ 213	$ 199
Post-Modification Outstanding Loan Balance	$ 126	$ 40	$ 201	$ 168
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	30	41	59	64
Pre-Modification Outstanding Loan Balance	$ 15	$ 29	$ 31	$ 38
Post-Modification Outstanding Loan Balance	$ 14	$ 31	$ 30	$ 39
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	105	144	253	500
Pre-Modification Outstanding Loan Balance	$ 20	$ 17	$ 37	$ 57
Post-Modification Outstanding Loan Balance	$ 20	$ 16	$ 36	$ 57
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	535	639	1,094	1,261
Pre-Modification Outstanding Loan Balance	$ 17	$ 15	$ 28	$ 26
Post-Modification Outstanding Loan Balance	$ 17	$ 14	$ 27	$ 23
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	7,461	8,146	16,007	17,551
Pre-Modification Outstanding Loan Balance	$ 37	$ 40	$ 80	$ 85
Post-Modification Outstanding Loan Balance	$ 38	$ 40	$ 81	$ 86
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	8,855	9,641	18,760	20,877
Pre-Modification Outstanding Loan Balance	$ 221	$ 163	$ 389	$ 405
Post-Modification Outstanding Loan Balance	$ 215	$ 141	$ 375	$ 373
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan		3		7
Pre-Modification Outstanding Loan Balance		$ 1		$ 2
Post-Modification Outstanding Loan Balance		$ 1		$ 2
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	2,248	1,043	3,136	3,972
Pre-Modification Outstanding Loan Balance	$ 298	$ 141	$ 415	$ 528
Post-Modification Outstanding Loan Balance	$ 295	$ 137	$ 408	$ 515

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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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