Loans - Delinquency Ratio for Consumer Loan (Detail) - USD ($) $ in Millions		Mar. 31, 2021		Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		$ 61,526		$ 62,088
Residential Mortgage Loan Delinquency Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell		273		281
Consumer Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		1,393		4,666
Fiscal year before current fiscal year		4,420		2,566
Two years before current fiscal year		2,343		1,465
Three years before current fiscal year		1,342		1,694
Four years before current fiscal year		1,546		1,985
Prior		8,343		6,991
Revolving Loans		987		1,122
Total loans		20,374		20,489
Mortgage Loans in Process of Foreclosure, Amount		102		109
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		1,365		4,529
Fiscal year before current fiscal year		4,289		2,476
Two years before current fiscal year		2,260		1,431
Three years before current fiscal year		1,308		1,658
Four years before current fiscal year		1,511		1,930
Prior		7,692		6,353
Revolving Loans		0		0
Total loans		18,425		18,377
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		3		50
Fiscal year before current fiscal year		51		51
Two years before current fiscal year		50		34
Three years before current fiscal year		33		35
Four years before current fiscal year		34		47
Prior		527		510
Revolving Loans		0		0
Total loans		698		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		937		1,066
Total loans		937		1,066
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year		25		87
Fiscal year before current fiscal year		80		39
Two years before current fiscal year		33		0
Three years before current fiscal year		1		1
Four years before current fiscal year		1		8
Prior		124		128
Revolving Loans		50		56
Total loans	[1]	314		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		8		16
Two years before current fiscal year		20		13
Three years before current fiscal year		21		25
Four years before current fiscal year		28		19
Prior		355		354
Revolving Loans		38		30
Total loans		470		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	[2],[3]	3
Fiscal year before current fiscal year		7	[2],[3]	15
Two years before current fiscal year		19	[2],[3]	13
Three years before current fiscal year		21	[2],[3]	25
Four years before current fiscal year		28	[2],[3]	19
Prior		325	[2],[3]	329
Revolving Loans		0	[2],[3]	0
Total loans	[2],[3]	400		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	[2],[3]	0
Fiscal year before current fiscal year		0	[2],[3]	0
Two years before current fiscal year		0	[2],[3]	0
Three years before current fiscal year		0	[2],[3]	0
Four years before current fiscal year		0	[2],[3]	0
Prior		25	[2],[3]	25
Revolving Loans		0	[2],[3]	0
Total loans	[2],[3]	25		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		36		28
Total loans		36		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		1		1
Two years before current fiscal year		1		0
Three years before current fiscal year		0		0
Four years before current fiscal year		0		0
Prior		5		0
Revolving Loans		2		2
Total loans		$ 9		$ 8

[1] Includes certain student loans that we have elected to designate under the fair value option and are therefore carried at fair value, which totaled $30 million and $32 million at March 31, 2021 and December 31, 2020, respectively. See Note 10, "Fair Value Option," for further details.

[2] At March 31, 2021 and December 31, 2020, consumer mortgage loans include $102 million and $109 million, respectively, of loans that were in the process of foreclosure.

[3] At March 31, 2021 and December 31, 2020, consumer mortgage loan delinquency includes $273 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.