Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs in the Past Twelve Months that have Subsequently Defaulted (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 SecurityLoan	Mar. 31, 2014 SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans	2,182	2,024
Amount Defaulted	$ 54	$ 61
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	164	145
Amount Defaulted	2	5
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	5	6
Amount Defaulted	2	7
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	106	148
Amount Defaulted	13	22
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1,578	1,461
Amount Defaulted	8	8
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	131	185
Amount Defaulted	3	6
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1,984	1,945
Amount Defaulted	28	48
Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	198	71
Amount Defaulted	26	10
Covered Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans		8
Amount Defaulted		$ 3