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		9 Months Ended
	Sep. 30, 2017 USD ($) SecurityLoan	Sep. 30, 2016 USD ($) SecurityLoan	Sep. 30, 2017 USD ($) SecurityLoan	Sep. 30, 2016 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,814	1,931	7,974	5,683
Amount Defaulted | $	$ 91	$ 25	$ 206	$ 76
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	200	121	555	374
Amount Defaulted | $	$ 25	$ 4	$ 49	$ 15
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	10	6	28	21
Amount Defaulted | $	$ 3	$ 3	$ 6	$ 9
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	84	43	251	101
Amount Defaulted | $	$ 7	$ 4	$ 26	$ 13
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	89	103	320	269
Amount Defaulted | $	$ 1	$ 1	$ 4	$ 5
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,076	1,617	6,107	4,822
Amount Defaulted | $	$ 9	$ 7	$ 26	$ 21
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,459	1,890	7,261	5,587
Amount Defaulted | $	$ 45	$ 19	$ 111	$ 63
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1	2	2	3
Amount Defaulted | $		$ 1		$ 1
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	354	39	711	93
Amount Defaulted | $	$ 46	$ 5	$ 95	$ 12