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	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 278,990	$ 277,492
Accruing 30-89 Days Past Due	1,107	1,212
Accruing 90 Days or More Past Due	551	720
Nonperforming	813	1,008
Total loans, excluding covered loans	280,061	277,311
Total loans	281,461	280,432
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	98,765	97,005
Accruing 30-89 Days Past Due	230	250
Accruing 90 Days or More Past Due	62	57
Nonperforming	216	249
Total loans, excluding covered loans	99,273	97,561
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	39,828	40,279
Accruing 30-89 Days Past Due	30	36
Accruing 90 Days or More Past Due	3	6
Nonperforming	105	142
Total loans, excluding covered loans	39,966	40,463
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	62,302	59,013
Accruing 30-89 Days Past Due	167	198
Accruing 90 Days or More Past Due	118	130
Nonperforming	317	442
Total loans, excluding covered loans	62,904	59,783
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	55,412	56,685
Accruing 30-89 Days Past Due	365	376
Accruing 90 Days or More Past Due	97	95
Nonperforming	175	168
Total loans, excluding covered loans	56,049	57,324
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	21,301	21,593
Accruing 30-89 Days Past Due	309	302
Accruing 90 Days or More Past Due	259	284
Nonperforming		1
Total loans, excluding covered loans	21,869	22,180
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	277,608	274,575
Accruing 30-89 Days Past Due	1,101	1,162
Accruing 90 Days or More Past Due	539	572
Nonperforming	813	1,002
Total loans, excluding covered loans	280,061	277,311
Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,382	2,917
Accruing 30-89 Days Past Due	6	50
Accruing 90 Days or More Past Due	12	148
Nonperforming		6
Total loans	$ 1,400	$ 3,121