Loans and Allowance for Credit Losses - Impaired Loans Average Recorded Investment and Interest Income Recognized (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 4,792	$ 5,466	$ 4,856	$ 5,494
Interest Income Recognized	40	55	80	110
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	514	720	530	769
Interest Income Recognized	1	1	2	2
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	242	272	255	275
Interest Income Recognized	2	3	4	5
Residential Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,846	2,182	1,880	2,211
Interest Income Recognized	19	28	39	57
Other Retail [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	303	279	301	279
Interest Income Recognized	4	3	8	7
Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	234	229	233	227
Interest Income Recognized	1	1	2	2
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	3,139	3,682	3,199	3,761
Interest Income Recognized	27	36	55	73
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	37	38	37	37
Interest Income Recognized	1		1
Government National Mortgage Association [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,616	1,746	1,620	1,696
Interest Income Recognized	$ 12	$ 19	$ 24	$ 37