Trading Cash Instruments - Additional Information (Detail) - Trading Cash Instruments Assets Fair Value Disclosure [Member] - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Net gains / (losses) on assets | $ (77) | $ 54 |
| Net realized gains / (losses) on assets | 66 | 89 |
| Net unrealized gains / (losses) on assets relating to instruments still held at the reporting date | (143) | (35) |
| Market making [Member] | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Net gains / (losses) on assets | (193) | (56) |
| Interest Income [Member] | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Net gains / (losses) on assets | $ 116 | $ 110 |