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, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 289,237	$ 284,109
Accruing 30-89 Days Past Due	1,236	1,300
Accruing 90 Days or More Past Due	752	584
Nonperforming	803	817
Total loans	292,028	286,810
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	103,075	101,844
Accruing 30-89 Days Past Due	353	322
Accruing 90 Days or More Past Due	273	69
Nonperforming	279	209
Total loans	103,980	102,444
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	39,214	39,354
Accruing 30-89 Days Past Due	27	70
Accruing 90 Days or More Past Due	1
Nonperforming	92	115
Total loans	39,334	39,539
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	67,353	64,443
Accruing 30-89 Days Past Due	184	181
Accruing 90 Days or More Past Due	113	114
Nonperforming	263	296
Total loans	67,913	65,034
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	56,724	55,722
Accruing 30-89 Days Past Due	384	403
Accruing 90 Days or More Past Due	98	108
Nonperforming	169	197
Total loans	57,375	56,430
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,871	22,746
Accruing 30-89 Days Past Due	288	324
Accruing 90 Days or More Past Due	267	293
Total loans	$ 23,426	$ 23,363