Newly-Formed Joint Ventures, Acquisitions and Divestitures - Additional Information Acquisitions (Details) - Permian Acquisition [Member] - USD ($)			3 Months Ended	9 Months Ended
	May 30, 2017	Mar. 01, 2017	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired		100.00%
Cash payments related to acquisition		$ 484,100,000
Acquired debt and all other assumed liabilities included in purchase consideration	$ 90,000,000
Additional cash that may be paid based on potential earn-out payment						$ 317,000,000
Acquisition-related expenses			$ 5,600,000	$ 5,600,000
Maximum [Member]
Business Acquisition [Line Items]
Additional cash that may be paid based on potential earn-out payment		$ 935,000,000			$ 935,000,000