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, 2016 USD ($) SecurityLoan	Jun. 30, 2015 USD ($) SecurityLoan	Jun. 30, 2016 USD ($) SecurityLoan	Jun. 30, 2015 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans	1,922	2,082	3,752	4,264
Amount Defaulted | $	$ 28	$ 63	$ 51	$ 117
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	141	149	253	313
Amount Defaulted | $	$ 9	$ 17	$ 11	$ 19
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	5	3	15	8
Amount Defaulted | $	$ 1	$ 1	$ 6	$ 3
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	27	80	58	186
Amount Defaulted | $	$ 4	$ 12	$ 9	$ 25
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	88	237	166	368
Amount Defaulted | $	$ 3	$ 4	$ 4	$ 7
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1,632	1,443	3,205	3,021
Amount Defaulted | $	$ 7	$ 7	$ 14	$ 15
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1,893	1,912	3,697	3,896
Amount Defaulted | $	$ 24	$ 41	$ 44	$ 69
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1		1
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	28	170	54	368
Amount Defaulted | $	$ 4	$ 22	$ 7	$ 48