Loans - Delinquency Ratio for Consumer Loan (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Residential Mortgage Loan Delinquency Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell	$ 249	$ 256
Consumer Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,087
2019	3,093
2018	1,850
2017	2,105
2016	2,428
Prior	8,521
Revolving Loans	1,398
Total loans	20,482	20,342
Mortgage Loans in Process of Foreclosure, Amount	135	142
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,032
2019	2,976
2018	1,805
2017	2,062
2016	2,371
Prior	7,788
Revolving Loans	0
Total loans	18,034	17,801
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	14
2019	54
2018	44
2017	41
2016	53
Prior	608
Revolving Loans	0
Total loans	814	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	1,300
Total loans	1,300	1,405
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	41
2019	63
2018	1
2017	2
2016	4
Prior	125
Revolving Loans	98
Total loans	334	283
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	12
2018	10
2017	15
2016	13
Prior	345
Revolving Loans	41
Total loans	436	416
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Residential Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	11
2018	10
2017	15
2016	13
Prior	315
Revolving Loans	0
Total loans	364	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	26
Revolving Loans	0
Total loans	26	25
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [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	39
Total loans	39	34
Consumer Loans [Member] | Contractual Delinquency, 60 Days or More Past Due [Member] | Other consumer [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1
2018	0
2017	0
2016	0
Prior	4
Revolving Loans	2
Total loans	$ 7	$ 7