Loans - Summary of TDRs in Consumer Portfolio (Detail) - USD ($) $ in Millions		Sep. 30, 2021		Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Total loans		$ 55,526		$ 62,088
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		3,598		4,666
Fiscal year before current fiscal year		3,613		2,566
Two years before current fiscal year		1,785		1,465
Three years before current fiscal year		971		1,694
Four years before current fiscal year		1,096		1,985
Prior		5,547		6,991
Revolving Loans		2		1,122
Total loans	[1]	16,612	[2]	20,489
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		3,580		4,529
Fiscal year before current fiscal year		3,566		2,476
Two years before current fiscal year		1,751		1,431
Three years before current fiscal year		951		1,658
Four years before current fiscal year		1,076		1,930
Prior		5,169		6,353
Revolving Loans		0		0
Total loans		16,093		18,377
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		12		50
Fiscal year before current fiscal year		34		51
Two years before current fiscal year		29		34
Three years before current fiscal year		19		35
Four years before current fiscal year		19		47
Prior		256		510
Revolving Loans		0		0
Total loans		369		727
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		0		0
Fiscal year before current fiscal year		0		0
Two years before current fiscal year		0		0
Three years before current fiscal year		0		0
Four years before current fiscal year		0		0
Prior		0		0
Revolving Loans		0		1,066
Total loans		0		1,066
Consumer Loans [Member] | Troubled Debt Restructuring [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		0		3
Fiscal year before current fiscal year		1		5
Two years before current fiscal year		3		6
Three years before current fiscal year		6		3
Four years before current fiscal year		1		2
Prior		390		594
Revolving Loans		0		5
Total loans		401		618
Consumer Loans [Member] | Troubled Debt Restructuring [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		0		3
Fiscal year before current fiscal year		1		5
Two years before current fiscal year		3		6
Three years before current fiscal year		6		3
Four years before current fiscal year		1		2
Prior		373		563
Revolving Loans		0		0
Total loans		384		582
Consumer Loans [Member] | Troubled Debt Restructuring [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		0		0
Fiscal year before current fiscal year		0		0
Two years before current fiscal year		0		0
Three years before current fiscal year		0		0
Four years before current fiscal year		0		0
Prior		17		31
Revolving Loans		0		0
Total loans		17		31
Consumer Loans [Member] | Troubled Debt Restructuring [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year		0		0
Fiscal year before current fiscal year		0		0
Two years before current fiscal year		0		0
Three years before current fiscal year		0		0
Four years before current fiscal year		0		0
Prior		0		0
Revolving Loans		0		5
Total loans		$ 0		$ 5

[1] The decrease in loans at September 30, 2021 includes the impact of our decision to exit our mass market retail banking business as well as our remaining retail credit card portfolio which resulted in the transfer of certain loans to held for sale during the second quarter of 2021. See Note 8, "Loans Held for Sale," for additional information.

[2] The decrease in past due loans at September 30, 2021 includes the impact of our decision to exit our mass market retail banking business as well as our remaining retail credit card portfolio which resulted in the transfer of certain loans to held for sale during the second quarter of 2021, including $115 million of consumer loans which were past due 30 days or more.