Collateralized Transactions (Narrative) (Details) - USD ($) $ in Millions |
Mar. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Disclosure Collateralized Transactions [Abstract] | ||
| Customers receivables | $ 15,222 | $ 17,050 |
| Securities repledged and deposited for customers | $ 1,400 | $ 600 |
| Percentage of securities repledged and deposited for customers | 64.00% | 76.00% |