Supplemental Cash Flow Information (Details) - USD ($) $ in Millions			3 Months Ended
		May 30, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 01, 2017
Cash:
Interest paid, net of capitalized interest	[1]		$ 42.8	$ 56.1
Income taxes paid, net of refunds				(0.2)
Non-cash investing activities:
Deadstock commodity inventory transferred to property, plant and equipment			1.7	8.3
Impact of capital expenditure accruals on property, plant and equipment			(22.3)	30.0
Transfers from materials and supplies inventory to property, plant and equipment			0.4	0.4
Contribution of property, plant and equipment to investments in unconsolidated affiliates			16.0	1.0
Change in ARO liability and property, plant and equipment due to revised cash flow estimate			2.1	1.7
Non-cash financing activities:
Reduction of Owner's Equity related to accrued dividends on unvested equity awards under share compensation arrangements			3.3	2.2
Receivables from equity offerings				19.6
Accretion of deemed dividends on Series A Preferred Stock			7.0	6.1
Impact of accounting standard adoption recorded in retained earnings			5.2	56.1
Non-cash balance sheet movements related to acquisition of related party:
Noncontrolling interest			1.2
Permian Acquisition [Member]
Non-cash balance sheet movements related to the Permian Acquisition (See Note 4 - Newly-Formed Joint Ventures and Acquisitions):
Potential earn-out payments of acquisition date fair value			$ 416.3	461.6	$ 416.3
Acquired debt and all other assumed liabilities included in purchase consideration		$ 90.0		$ 90.0

[1] Interest capitalized on major projects was $9.6 million and $1.7 million for the three months ended March 31, 2018 and 2017.