Other Long-term Liabilities, Contingent Consideration (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Mar. 01, 2017
Other Liabilities Noncurrent [Line Items]
Decrease in fair value of contingent liability	$ (56,100,000)	$ (3,300,000)
Permian Acquisition [Member]
Other Liabilities Noncurrent [Line Items]
Preliminary acquisition date fair value of the contingent consideration	416,300,000	461,600,000		$ 416,300,000
Decrease in fair value of contingent liability	(56,000,000)	$ (3,200,000)	$ 99,300,000
Additional cash paid in potential earn-out payment	373,000,000		$ 317,000,000
Permian Acquisition [Member] | Accounts Payable and Accrued Liabilities [Member]
Other Liabilities Noncurrent [Line Items]
Fair value of first potential earn-out payment	0
Permian Acquisition [Member] | Other Long-term Liabilities [Member]
Other Liabilities Noncurrent [Line Items]
Fair value of second potential earn-out payment	$ 373,000,000