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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 5,236	$ 5,557	$ 5,408	$ 5,784
Interest Income Recognized	52	65	162	195
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	624	845	720	786
Interest Income Recognized	3	2	5	6
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	272	334	274	321
Interest Income Recognized	2	6	7	12
Residential Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	2,111	2,381	2,178	2,457
Interest Income Recognized	25	30	82	93
Other Retail [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	288	287	282	296
Interest Income Recognized	4	3	11	9
Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	231	214	229	212
Interest Income Recognized	1	1	3	3
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	3,526	4,061	3,683	4,072
Interest Income Recognized	35	42	108	123
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	38	38	37	38
Interest Income Recognized				1
Government National Mortgage Association [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,672	1,458	1,688	1,674
Interest Income Recognized	$ 17	$ 23	$ 54	$ 71