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, 2016 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2016 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,931	1,988	5,683	6,252
Amount Defaulted | $	$ 25	$ 37	$ 76	$ 154
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	121	95	374	408
Amount Defaulted | $	$ 4	$ 1	$ 15	$ 20
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	6	5	21	13
Amount Defaulted | $	$ 3	$ 5	$ 9	$ 8
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	43	42	101	228
Amount Defaulted | $	$ 4	$ 5	$ 13	$ 30
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	103	123	269	491
Amount Defaulted | $	$ 1	$ 2	$ 5	$ 9
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,617	1,576	4,822	4,597
Amount Defaulted | $	$ 7	$ 7	$ 21	$ 22
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,890	1,841	5,587	5,737
Amount Defaulted | $	$ 19	$ 20	$ 63	$ 89
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2	4	3	4
Amount Defaulted | $	$ 1	$ 1	$ 1	$ 1
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	39	143	93	511
Amount Defaulted | $	$ 5	$ 16	$ 12	$ 64