Other Long-term Liabilities - Schedule of Changes in Contingent Consideration (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Other Liabilities Noncurrent [Line Items]
Increase in fair value due to factors occurring after acquisition date	$ 56.1	$ 3.3
Permian Acquisition [Member]
Other Liabilities Noncurrent [Line Items]
Balance at December 31, 2017	317.0
Increase in fair value due to factors occurring after acquisition date	56.0	$ 3.2	$ (99.3)
Balance at March 31, 2018	373.0		317.0
Less: Current portion	(373.0)		(6.8)
Long-term balance at March 31, 2018	$ 373.0		$ 310.2