Business Segments - Summary of Gross Loans by Segment and Loan (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Loans	$ 115,557	$ 110,345
Investment Banking [Member]
Segment Reporting Information [Line Items]
Loans	31,548	27,035
Global Markets [Member]
Segment Reporting Information [Line Items]
Loans	29,445	31,279
Asset Management [Member]
Segment Reporting Information [Line Items]
Loans	17,708	17,486
Consumer & Wealth Management [Member]
Segment Reporting Information [Line Items]
Loans	36,856	34,545
Corporate [Member]
Segment Reporting Information [Line Items]
Loans	51,465	46,307
Corporate [Member] | Investment Banking [Member]
Segment Reporting Information [Line Items]
Loans	31,548	27,035
Corporate [Member] | Global Markets [Member]
Segment Reporting Information [Line Items]
Loans	11,860	11,852
Corporate [Member] | Asset Management [Member]
Segment Reporting Information [Line Items]
Loans	8,057	7,420
Real Estate [Member] | Global Markets [Member]
Segment Reporting Information [Line Items]
Loans	14,134	15,671
Real Estate [Member] | Asset Management [Member]
Segment Reporting Information [Line Items]
Loans	8,948	9,030
Other Loans [Member]
Segment Reporting Information [Line Items]
Loans	4,154	4,792
Other Loans [Member] | Global Markets [Member]
Segment Reporting Information [Line Items]
Loans	3,451	3,756
Other Loans [Member] | Asset Management [Member]
Segment Reporting Information [Line Items]
Loans	703	1,036
Wealth Management [Member] | Consumer & Wealth Management [Member]
Segment Reporting Information [Line Items]
Loans	29,836	27,940
Installment [Member]
Segment Reporting Information [Line Items]
Loans	4,112	4,747
Installment [Member] | Consumer & Wealth Management [Member]
Segment Reporting Information [Line Items]
Loans	4,112	4,747
Credit Card Receivable [Member]
Segment Reporting Information [Line Items]
Loans	2,908	1,858
Credit Card Receivable [Member] | Consumer & Wealth Management [Member]
Segment Reporting Information [Line Items]
Loans	$ 2,908	$ 1,858