Related Party Agreements and Transactions - Summary of Fees Received for Operating Pipelines for Related Parties Included in Other Income - Related Parties (Detail) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2015 |
Sep. 30, 2014 |
Sep. 30, 2015 |
Sep. 30, 2014 |
|
| Related Party Transaction [Line Items] | ||||
| Other income - related parties | $ 6.3 | $ 5.8 | $ 18.8 | $ 16.9 |
| MPC [Member] | ||||
| Related Party Transaction [Line Items] | ||||
| Other income - related parties | 6.1 | 5.5 | 17.9 | 16.0 |
| Centennial [Member] | ||||
| Related Party Transaction [Line Items] | ||||
| Other income - related parties | 0.2 | 0.3 | 0.8 | 0.8 |
| Muskegon [Member] | ||||
| Related Party Transaction [Line Items] | ||||
| Other income - related parties | $ 0.0 | $ 0.0 | $ 0.1 | $ 0.1 |