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
	Mar. 31, 2016 USD ($) SecurityLoan	Mar. 31, 2015 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,830	2,182
Amount Defaulted | $	$ 23	$ 54
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	112	164
Amount Defaulted | $	$ 2	$ 2
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	10	5
Amount Defaulted | $	$ 5	$ 2
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	31	106
Amount Defaulted | $	$ 5	$ 13
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	78	131
Amount Defaulted | $	$ 1	$ 3
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,573	1,578
Amount Defaulted | $	$ 7	$ 8
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,804	1,984
Amount Defaulted | $	$ 20	$ 28
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	26	198
Amount Defaulted | $	$ 3	$ 26