Significant Accounting Policies - Summary of Changes in Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	$ 1,761.2
Product sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	1,499.2	$ 990.0
Product sales—related parties
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	3.6	42.7
Midstream services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	92.2	127.4
Midstream services—related parties
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	166.2	$ 159.0
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	(138.0)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Product sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	(32.0)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Product sales—related parties
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	(22.0)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Midstream services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	(77.0)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 | Midstream services—related parties
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	$ (7.0)