Loans - Summary of TDRs in Consumer Portfolio (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Total loans	$ 61,526	$ 62,088
Consumer Loans [Member]
Financing Receivable, Impaired [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
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [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, Impaired [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, Impaired [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] | Troubled Debt Restructuring [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year	0	3
Fiscal year before current fiscal year	3	5
Two years before current fiscal year	6	6
Three years before current fiscal year	11	3
Four years before current fiscal year	3	2
Prior	593	594
Revolving Loans	5	5
Total loans	621	618
Consumer Loans [Member] | Troubled Debt Restructuring [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Current fiscal year	0	3
Fiscal year before current fiscal year	3	5
Two years before current fiscal year	6	6
Three years before current fiscal year	11	3
Four years before current fiscal year	3	2
Prior	562	563
Revolving Loans	0	0
Total loans	585	582
Consumer Loans [Member] | Troubled Debt Restructuring [Member] | Home Equity Mortgages [Member]
Financing Receivable, Impaired [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	31	31
Revolving Loans	0	0
Total loans	31	31
Consumer Loans [Member] | Troubled Debt Restructuring [Member] | Credit Cards [Member]
Financing Receivable, Impaired [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	5	5
Total loans	$ 5	$ 5