Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Millions |
Sep. 30, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Property, Plant and Equipment [Line Items] | ||
| Gross property, plant and equipment | $ 1,496.7 | $ 1,361.7 |
| Less accumulated depreciation | 387.5 | 353.1 |
| Net property, plant and equipment | 1,109.2 | 1,008.6 |
| Land [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Gross property, plant and equipment | 5.5 | 5.5 |
| Pipelines and Related Assets [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Gross property, plant and equipment | 1,085.0 | 1,081.4 |
| Storage and Delivery Facilities [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Gross property, plant and equipment | 197.7 | 165.8 |
| Assets Under Construction [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Gross property, plant and equipment | 184.3 | 85.3 |
| Other [Member] | ||
| Property, Plant and Equipment [Line Items] | ||
| Gross property, plant and equipment | $ 24.2 | $ 23.7 |