Investments in Unconsolidated Affiliates (Summarized Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Operating Revenues	$ 1,226.3	$ 519.2	$ 3,188.6	$ 1,599.8
Operating Expenses	140.6	132.7	359.8	448.5
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ (39.6)	$ 4.6	(116.0)	(43.1)
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Operating Revenues			313.8	206.5
Operating Expenses			665.1	171.9
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest			(350.6)	35.5
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Stagecoach Gas Services LLC
Schedule of Equity Method Investments [Line Items]
Operating Revenues			81.4	115.3
Operating Expenses			456.9	58.9
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest			(375.5)	56.5
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Other Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Operating Revenues			232.4	91.2
Operating Expenses			208.2	113.0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest			$ 24.9	$ (21.0)