Trading Cash Instruments - Additional Information (Detail) - Trading Cash Instruments Assets Fair Value Disclosure [Member] - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2021 |
Jun. 30, 2020 |
Jun. 30, 2021 |
Jun. 30, 2020 |
|
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||
| Net gains / (losses) on assets | $ 33 | $ (23) | $ 58 | $ (122) |
| Net realized gains / (losses) on assets | 23 | 17 | 42 | 68 |
| Net unrealized gains / (losses) on assets relating to instruments still held at the reporting date | 10 | (40) | 16 | (190) |
| Market making [Member] | ||||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||
| Net gains / (losses) on assets | (2) | (56) | (10) | (194) |
| Interest Income [Member] | ||||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||
| Net gains / (losses) on assets | $ 35 | $ 33 | $ 68 | $ 72 |