Segment And Geographic Information (Segment Table) (Details) - USD ($) $ in Millions |
3 Months Ended | ||
|---|---|---|---|
Mar. 31, 2016 |
Mar. 31, 2015 |
Dec. 31, 2015 |
|
| Segment Reporting Information [Line Items] | |||
| Net revenues | $ 489 | $ 172 | |
| Income before income taxes | 337 | (111) | |
| Assets | 50,186 | $ 48,734 | |
| Electronic Brokerage [Member] | |||
| Segment Reporting Information [Line Items] | |||
| Net revenues | 347 | 290 | |
| Income before income taxes | 235 | 51 | |
| Assets | 45,784 | 44,421 | |
| Market Making [Member] | |||
| Segment Reporting Information [Line Items] | |||
| Net revenues | 59 | 67 | |
| Income before income taxes | 20 | 27 | |
| Assets | 11,170 | 10,825 | |
| Corporate And Eliminations [Member] | |||
| Segment Reporting Information [Line Items] | |||
| Net revenues | 83 | (185) | |
| Income before income taxes | 82 | $ (189) | |
| Assets | $ (6,768) | $ (6,512) | |