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Trading Cash Instruments - Additional Information (Detail) - Trading Cash Instruments Assets Fair Value Disclosure [Member] - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Net gains / (losses) on assets $ 125 $ 14
Net realized gains / (losses) on assets 34 25
Net unrealized gains / (losses) on assets relating to instruments still held at the reporting date 159 11
Market making [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Net gains / (losses) on assets (158) (26)
Interest Income [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Net gains / (losses) on assets 37 $ 40
Investment Banking [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Net gains / (losses) on assets $ (4)