Loans - Delinquency Ratio for Consumer Loan (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		$ 66,409	$ 68,553
Residential Mortgage Loan Delinquency Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell		283	256
Consumer Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		3,661
2019		2,737
2018		1,572
2017		1,826
2016		2,137
Prior		7,527
Revolving Loans		1,166
Total loans		20,626	20,342
Mortgage Loans in Process of Foreclosure, Amount		115	142
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		3,546
2019		2,638
2018		1,531
2017		1,789
2016		2,084
Prior		6,851
Revolving Loans		0
Total loans		18,439	17,801
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		42
2019		54
2018		40
2017		37
2016		48
Prior		544
Revolving Loans		0
Total loans		765	853
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		0
2019		0
2018		0
2017		0
2016		0
Prior		0
Revolving Loans		1,107
Total loans		1,107	1,405
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		73
2019		45
2018		1
2017		0
2016		5
Prior		132
Revolving Loans		59
Total loans	[1]	315	283
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		8
2019		20
2018		21
2017		24
2016		25
Prior		369
Revolving Loans		27
Total loans		494	416
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		7
2019		20
2018		21
2017		24
2016		25
Prior		334
Revolving Loans		0
Total loans		431	350
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Home Equity Mortgages [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		0
2019		0
2018		0
2017		0
2016		0
Prior		31
Revolving Loans		0
Total loans		31	25
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Credit Cards [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020
2019
2018
2017
2016
Prior
Revolving Loans		25
Total loans		25	34
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020		1
2019		0
2018		0
2017		0
2016		0
Prior		4
Revolving Loans		2
Total loans		$ 7	$ 7

[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 $34 million at September 30, 2020. See Note 10, "Fair Value Option," for further details.