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	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 277,565	$ 277,492
Accruing 30-89 Days Past Due	1,060	1,212
Accruing 90 Days or More Past Due	640	720
Nonperforming	912	1,008
Total loans, excluding covered loans	277,354	277,311
Total loans	280,177	280,432
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	98,847	97,005
Accruing 30-89 Days Past Due	228	250
Accruing 90 Days or More Past Due	58	57
Nonperforming	224	249
Total loans, excluding covered loans	99,357	97,561
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	39,250	40,279
Accruing 30-89 Days Past Due	42	36
Accruing 90 Days or More Past Due	3	6
Nonperforming	104	142
Total loans, excluding covered loans	39,399	40,463
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	60,636	59,013
Accruing 30-89 Days Past Due	160	198
Accruing 90 Days or More Past Due	113	130
Nonperforming	400	442
Total loans, excluding covered loans	61,309	59,783
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	55,134	56,685
Accruing 30-89 Days Past Due	320	376
Accruing 90 Days or More Past Due	91	95
Nonperforming	178	168
Total loans, excluding covered loans	55,723	57,324
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	21,054	21,593
Accruing 30-89 Days Past Due	263	302
Accruing 90 Days or More Past Due	249	284
Nonperforming		1
Total loans, excluding covered loans	21,566	22,180
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	274,921	274,575
Accruing 30-89 Days Past Due	1,013	1,162
Accruing 90 Days or More Past Due	514	572
Nonperforming	906	1,002
Total loans, excluding covered loans	277,354	277,311
Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,644	2,917
Accruing 30-89 Days Past Due	47	50
Accruing 90 Days or More Past Due	126	148
Nonperforming	6	6
Total loans	$ 2,823	$ 3,121