Related Party Transactions - Payables To Related Parties (Detail) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Related Party Transaction [Line Items] | ||
| Payables to related parties | $ 51 | $ 69 |
| Illinois Extension Pipeline | ||
| Related Party Transaction [Line Items] | ||
| Payables to related parties | 7 | 8 |
| LOOP | ||
| Related Party Transaction [Line Items] | ||
| Payables to related parties | 2 | 3 |
| MarkWest Utica EMG | ||
| Related Party Transaction [Line Items] | ||
| Payables to related parties | 20 | 29 |
| Ohio Gathering | ||
| Related Party Transaction [Line Items] | ||
| Payables to related parties | 1 | 9 |
| Sherwood Midstream | ||
| Related Party Transaction [Line Items] | ||
| Payables to related parties | 11 | 8 |
| Other equity method investees | ||
| Related Party Transaction [Line Items] | ||
| Payables to related parties | $ 10 | $ 12 |