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, 2017 USD ($) SecurityLoan	Mar. 31, 2016 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,647	1,830
Amount Defaulted | $	$ 60	$ 23
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	173	112
Amount Defaulted | $	$ 8	$ 2
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	8	10
Amount Defaulted | $	$ 2	$ 5
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	72	31
Amount Defaulted | $	$ 9	$ 5
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	129	78
Amount Defaulted | $	$ 2	$ 1
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,047	1,573
Amount Defaulted | $	$ 9	$ 7
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,429	1,804
Amount Defaulted | $	$ 30	$ 20
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	218	26
Amount Defaulted | $	$ 30	$ 3