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, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,988	2,493	6,252	6,527
Amount Defaulted	$ 37	$ 112	$ 154	$ 221
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	95	161	408	456
Amount Defaulted	$ 1	$ 34	$ 20	$ 42
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	5	4	13	16
Amount Defaulted	$ 5		$ 8	$ 10
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	42	147	228	424
Amount Defaulted	$ 5	$ 22	$ 30	$ 61
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,576	1,665	4,597	4,586
Amount Defaulted	$ 7	$ 9	$ 22	$ 25
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	123	146	491	489
Amount Defaulted	$ 2	$ 5	$ 9	$ 15
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,841	2,123	5,737	5,971
Amount Defaulted	$ 20	$ 70	$ 89	$ 153
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	4	4	4	14
Amount Defaulted	$ 1	$ 1	$ 1	$ 5
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	143	366	511	542
Amount Defaulted	$ 16	$ 41	$ 64	$ 63