Loans and Allowance for Credit Losses - Impaired Loans Average Recorded Investment and Interest Income Recognized (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 4,762	$ 5,236	$ 4,825	$ 5,408
Interest Income Recognized	42	52	122	162
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	470	624	510	720
Interest Income Recognized	3	3	5	5
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	279	272	263	274
Interest Income Recognized	4	2	8	7
Residential Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,779	2,111	1,846	2,178
Interest Income Recognized	18	25	57	82
Other Retail [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	309	288	304	282
Interest Income Recognized	4	4	12	11
Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	236	231	234	229
Interest Income Recognized	1	1	3	3
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	3,073	3,526	3,157	3,683
Interest Income Recognized	30	35	85	108
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	23	38	33	37
Interest Income Recognized			1
Government National Mortgage Association [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,666	1,672	1,635	1,688
Interest Income Recognized	$ 12	$ 17	$ 36	$ 54