Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs in the Past Twelve Months that have Subsequently Defaulted (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	2,513	1,922	5,160	3,752
Amount Defaulted | $	$ 55	$ 28	$ 115	$ 51
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	182	141	355	253
Amount Defaulted | $	$ 16	$ 9	$ 24	$ 11
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	10	5	18	15
Amount Defaulted | $	$ 1	$ 1	$ 3	$ 6
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	95	27	167	58
Amount Defaulted | $	$ 10	$ 4	$ 19	$ 9
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	102	88	231	166
Amount Defaulted | $	$ 1	$ 3	$ 3	$ 4
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1,984	1,632	4,031	3,205
Amount Defaulted | $	$ 8	$ 7	$ 17	$ 14
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	2,373	1,893	4,802	3,697
Amount Defaulted | $	$ 36	$ 24	$ 66	$ 44
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1	1	1	1
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	139	28	357	54
Amount Defaulted | $	$ 19	$ 4	$ 49	$ 7