Loans - Delinquency Ratio for Consumer Loan (Detail) - USD ($) $ in Millions		Sep. 30, 2021		Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		$ 55,526		$ 62,088
Residential Mortgage Loan Delinquency Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell		252		281
Consumer Loans [Member]
Financing Receivable, Credit Quality Indicator [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
Mortgage Loans in Process of Foreclosure, Amount		91		109
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [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, Credit Quality Indicator [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, Credit Quality Indicator [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] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		6		87
Fiscal year before current fiscal year		13		39
Two years before current fiscal year		5		0
Three years before current fiscal year		1		1
Four years before current fiscal year		1		8
Prior		122		128
Revolving Loans		2		56
Total loans	[3]	150		319
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0		4
Fiscal year before current fiscal year		4		16
Two years before current fiscal year		12		13
Three years before current fiscal year		7		25
Four years before current fiscal year		19		19
Prior		292		358
Revolving Loans		0		30
Total loans		334		465
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0	[4],[5]	3
Fiscal year before current fiscal year		4	[4],[5]	15
Two years before current fiscal year		12	[4],[5]	13
Three years before current fiscal year		7	[4],[5]	25
Four years before current fiscal year		19	[4],[5]	19
Prior		268	[4],[5]	329
Revolving Loans		0	[4],[5]	0
Total loans	[4],[5]	310		404
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Home Equity Mortgages [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0	[4],[5]	0
Fiscal year before current fiscal year		0	[4],[5]	0
Two years before current fiscal year		0	[4],[5]	0
Three years before current fiscal year		0	[4],[5]	0
Four years before current fiscal year		0	[4],[5]	0
Prior		20	[4],[5]	25
Revolving Loans		0	[4],[5]	0
Total loans	[4],[5]	20		25
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Credit Cards [Member]
Financing Receivable, Credit Quality Indicator [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		28
Total loans		0		28
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		0		1
Fiscal year before current fiscal year		0		1
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		4		4
Revolving Loans		0		2
Total loans		$ 4		$ 8

[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.

[3] Includes certain student loans that we have elected to designate under the fair value option and are therefore carried at fair value, which totaled $27 million and $32 million at September 30, 2021 and December 31, 2020, respectively. See Note 11, "Fair Value Option," for further details.

[4] At September 30, 2021 and December 31, 2020, consumer mortgage loans include $91 million and $109 million, respectively, of loans that were in the process of foreclosure.

[5] At September 30, 2021 and December 31, 2020, consumer mortgage loan delinquency includes $252 million and $281 million, respectively, of loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell.