Revenue - Schedule of Changes in Technology and Risk Management Deferred Revenue Liability (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Revenue From Contract With Customer [Abstract] | ||
| Beginning balance | $ 62 | $ 42 |
| Additions | 12 | 8 |
| Amount recognized included in the deferred revenue liability beginning balance | (8) | (4) |
| Ending balance | $ 66 | $ 46 |