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, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 284,774	$ 284,109
Accruing 30-89 Days Past Due	1,472	1,300
Accruing 90 Days or More Past Due	595	584
Nonperforming	858	817
Total loans	287,699	286,810
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	102,125	101,844
Accruing 30-89 Days Past Due	596	322
Accruing 90 Days or More Past Due	77	69
Nonperforming	271	209
Total loans	103,069	102,444
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	39,248	39,354
Accruing 30-89 Days Past Due	43	70
Accruing 90 Days or More Past Due	3
Nonperforming	127	115
Total loans	39,421	39,539
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	65,666	64,443
Accruing 30-89 Days Past Due	168	181
Accruing 90 Days or More Past Due	122	114
Nonperforming	287	296
Total loans	66,243	65,034
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	56,045	55,722
Accruing 30-89 Days Past Due	375	403
Accruing 90 Days or More Past Due	105	108
Nonperforming	173	197
Total loans	56,698	56,430
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	21,690	22,746
Accruing 30-89 Days Past Due	290	324
Accruing 90 Days or More Past Due	288	293
Total loans	$ 22,268	$ 23,363