Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended
Mar. 31, 2017 USD ($) SecurityLoan	Mar. 31, 2016 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	14,169	12,371
Pre-Modification Outstanding Loan Balance	$ 630	$ 561
Post-Modification Outstanding Loan Balance	$ 611	$ 561
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	830	601
Pre-Modification Outstanding Loan Balance	$ 137	$ 160
Post-Modification Outstanding Loan Balance	$ 128	$ 161
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	23	24
Pre-Modification Outstanding Loan Balance	$ 9	$ 7
Post-Modification Outstanding Loan Balance	$ 8	$ 7
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	356	278
Pre-Modification Outstanding Loan Balance	$ 40	$ 32
Post-Modification Outstanding Loan Balance	$ 41	$ 32
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	622	609
Pre-Modification Outstanding Loan Balance	$ 11	$ 11
Post-Modification Outstanding Loan Balance	$ 9	$ 11
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	9,405	7,988
Pre-Modification Outstanding Loan Balance	$ 45	$ 38
Post-Modification Outstanding Loan Balance	$ 46	$ 39
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	11,236	9,500
Pre-Modification Outstanding Loan Balance	$ 242	$ 248
Post-Modification Outstanding Loan Balance	$ 232	$ 250
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	4	3
Pre-Modification Outstanding Loan Balance	$ 1
Post-Modification Outstanding Loan Balance	$ 1
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	2,929	2,868
Pre-Modification Outstanding Loan Balance	$ 387	$ 313
Post-Modification Outstanding Loan Balance	$ 378	$ 311

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+ 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=66008989&loc=SL6953676-111524

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