Significant Accounting Policies - Summary of Changes in Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	$ 1,779.9		$ 3,541.1
Product sales
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	1,435.1	$ 927.2	2,934.3	$ 1,917.2
Product sales—related parties
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	27.2	29.3	30.8	72.0
Midstream services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	142.4	131.9	234.6	259.3
Midstream services—related parties
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contracts with customers	175.2	$ 173.6	341.4	$ 332.6
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	(163.0)		(301.0)
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	(46.0)		(78.0)
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	(24.0)		(46.0)
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	(76.0)		(153.0)
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	$ (17.0)		$ (24.0)