Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 321.9	$ 307.5	$ 296.2	$ 280.6	$ 410.5	$ 560.8	$ 532.4	$ 428.9	$ 1,206.2	$ 1,932.6
As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues									1,187.4	1,871.3	$ 1,545.3
Williston Basin [Member] | As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues									438.9	765.7	680.3
Pinedale [Member] | As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues											204.6
Uinta Basin [Member] | As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues										55.1	85.5
Other Northern [Member] | As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues									1.6	6.9	21.8
Permian Basin [Member] | As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues									740.7	739.3	336.3
Haynesville [Member]
Disaggregation of Revenue [Line Items]
Revenues									5.9
Haynesville [Member] | As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues										304.1	216.0
Other Southern [Member] | As reported [Member]
Disaggregation of Revenue [Line Items]
Revenues									6.2	0.2	0.8
Oil and Condensate [Member]
Disaggregation of Revenue [Line Items]
Revenues									1,132.6	1,422.4	939.4
Oil and Condensate [Member] | Williston Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues									420.8	707.0	586.5
Oil and Condensate [Member] | Pinedale [Member]
Disaggregation of Revenue [Line Items]
Revenues											18.0
Oil and Condensate [Member] | Uinta Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues										25.3	29.6
Oil and Condensate [Member] | Other Northern [Member]
Disaggregation of Revenue [Line Items]
Revenues									1.1	4.9	4.9
Oil and Condensate [Member] | Permian Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues									710.6	684.4	298.8
Oil and Condensate [Member] | Haynesville [Member]
Disaggregation of Revenue [Line Items]
Revenues										1.0	1.2
Oil and Condensate [Member] | Other Southern [Member]
Disaggregation of Revenue [Line Items]
Revenues									0.1	(0.2)	0.4
Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues									52.4	393.1	494.0
Natural Gas [Member] | Williston Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues									33.1	45.3	42.3
Natural Gas [Member] | Pinedale [Member]
Disaggregation of Revenue [Line Items]
Revenues											154.8
Natural Gas [Member] | Uinta Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues										25.0	50.0
Natural Gas [Member] | Other Northern [Member]
Disaggregation of Revenue [Line Items]
Revenues									0.4	2.0	16.6
Natural Gas [Member] | Permian Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues									12.8	17.3	15.5
Natural Gas [Member] | Haynesville [Member]
Disaggregation of Revenue [Line Items]
Revenues										303.1	214.4
Natural Gas [Member] | Other Southern [Member]
Disaggregation of Revenue [Line Items]
Revenues									6.1	0.4	0.4
Natural Gas Liquids [Member]
Disaggregation of Revenue [Line Items]
Revenues									57.3	110.8	111.9
Natural Gas Liquids [Member] | Williston Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues									19.4	56.5	51.5
Natural Gas Liquids [Member] | Pinedale [Member]
Disaggregation of Revenue [Line Items]
Revenues											31.8
Natural Gas Liquids [Member] | Uinta Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues										4.8	5.9
Natural Gas Liquids [Member] | Other Northern [Member]
Disaggregation of Revenue [Line Items]
Revenues									0.1	0.0	0.3
Natural Gas Liquids [Member] | Permian Basin [Member]
Disaggregation of Revenue [Line Items]
Revenues									37.8	49.5	22.0
Natural Gas Liquids [Member] | Haynesville [Member]
Disaggregation of Revenue [Line Items]
Revenues										0.0	0.4
Natural Gas Liquids [Member] | Other Southern [Member]
Disaggregation of Revenue [Line Items]
Revenues									0.0	0.0	0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									(54.9)	(55.0)	0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member] | Williston Basin [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									(34.4)	(43.1)	0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member] | Pinedale [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold											0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member] | Uinta Basin [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold										0.0	0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member] | Other Northern [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									0.0	0.0	0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member] | Permian Basin [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									(20.5)	(11.9)	0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member] | Haynesville [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold										0.0	0.0
Natural Gas, Gathering, Transportation, Marketing and Processing [Member] | Other Southern [Member]
Disaggregation of Revenue [Line Items]
Cost of Goods and Services Sold									$ 0.0	$ 0.0	$ 0.0