Loans - Summary of TDRs in Consumer Portfolio (Detail) - Consumer Loans [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Impaired [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
Residential Mortgage [Member]
Financing Receivable, Impaired [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
Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
2020	14
2019	54
2018	44
2017	41
2016	53
Prior	608
Revolving Loans	0
Total loans	814	853
Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	1,300
Total loans	1,300	1,405
Troubled Debt Restructuring [Member]
Financing Receivable, Impaired [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	1
Prior	592
Revolving Loans	4
Total loans	597	616
Troubled Debt Restructuring [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	1
Prior	560
Revolving Loans	0
Total loans	561	580
Troubled Debt Restructuring [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	32
Revolving Loans	0
Total loans	32	32
Troubled Debt Restructuring [Member] | Credit Cards [Member]
Financing Receivable, Impaired [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	4
Total loans	$ 4	$ 4