Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class, Including Delinquency Status of those that Continue to Accrue Interest and are Nonperforming (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 275,118	$ 277,492
Accruing 30-89 Days Past Due	1,067	1,212
Accruing 90 Days or More Past Due	702	720
Nonperforming	1,024	1,008
Total loans, excluding covered loans	274,932	277,311
Total loans	277,911	280,432
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	97,494	97,005
Accruing 30-89 Days Past Due	241	250
Accruing 90 Days or More Past Due	61	57
Nonperforming	301	249
Total loans, excluding covered loans	98,097	97,561
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	39,979	40,279
Accruing 30-89 Days Past Due	38	36
Accruing 90 Days or More Past Due	4	6
Nonperforming	119	142
Total loans, excluding covered loans	40,140	40,463
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	59,769	59,013
Accruing 30-89 Days Past Due	146	198
Accruing 90 Days or More Past Due	132	130
Nonperforming	430	442
Total loans, excluding covered loans	60,477	59,783
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	54,730	56,685
Accruing 30-89 Days Past Due	320	376
Accruing 90 Days or More Past Due	99	95
Nonperforming	168	168
Total loans, excluding covered loans	55,317	57,324
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	20,356	21,593
Accruing 30-89 Days Past Due	275	302
Accruing 90 Days or More Past Due	270	284
Nonperforming		1
Total loans, excluding covered loans	20,901	22,180
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	272,328	274,575
Accruing 30-89 Days Past Due	1,020	1,162
Accruing 90 Days or More Past Due	566	572
Nonperforming	1,018	1,002
Total loans, excluding covered loans	274,932	277,311
Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,790	2,917
Accruing 30-89 Days Past Due	47	50
Accruing 90 Days or More Past Due	136	148
Nonperforming	6	6
Total loans	$ 2,979	$ 3,121