Related Party Transactions - Summarized Financial Information for Equity Method Investments (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Related Party Transactions [Abstract] | ||
| Revenues and other income | $ 1,132 | $ 1,027 |
| Income from operations | 73 | 82 |
| Net income | $ 71 | $ 81 |