Loans - Summary of Loans and Lending Commitments Accounted for at Amortized Cost by Portfolio (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 133,808	$ 119,989
Lending commitments	192,914	162,513
Corporate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	47,814	48,659
Wealth management [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	39,955	33,023
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,468	20,290
Residential real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,218	5,750
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,886	4,174
Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,257	3,823
Credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,210	4,270
Wholesale Portfolio Segment [Member] \| Corporate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	44,153	44,778
Lending commitments	148,973	127,756
Wholesale Portfolio Segment [Member] \| Wealth management [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	32,833	25,151
Lending commitments	3,382	2,314
Wholesale Portfolio Segment [Member] \| Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,321	17,096
Lending commitments	4,151	4,154
Wholesale Portfolio Segment [Member] \| Residential real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11,696	5,236
Lending commitments	2,410	1,804
Wholesale Portfolio Segment [Member] \| Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,841	3,211
Lending commitments	5,461	4,841
Consumer Portfolio Segment [Member] \| Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,257	3,823
Lending commitments	8	4
Consumer Portfolio Segment [Member] \| Credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,210	4,270
Lending commitments	28,529	21,640
Wholesale and Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	119,311	103,565
Lending commitments	$ 192,914	$ 162,513