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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 5,557	$ 6,092	$ 5,784	$ 6,227
Interest Income Recognized	65	65	195	207
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	845	408	786	351
Interest Income Recognized	2	3	6	9
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	334	388	321	461
Interest Income Recognized	6	3	12	13
Residential Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	2,381	2,669	2,457	2,687
Interest Income Recognized	30	31	93	97
Other Retail [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	287	329	296	342
Interest Income Recognized	3	3	9	10
Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	214	216	212	224
Interest Income Recognized	1	1	3	4
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	4,061	4,010	4,072	4,065
Interest Income Recognized	42	41	123	133
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	38	42	38	42
Interest Income Recognized			1
Government National Mortgage Association [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,458	2,040	1,674	2,120
Interest Income Recognized	$ 23	$ 24	$ 71	$ 74