Investments in Unconsolidated Affiliates (Summarized Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Apr. 09, 2019
Schedule of Equity Method Investments [Line Items]
Operating Revenues	$ 519.2	$ 823.6	$ 1,599.8	$ 2,342.2
Operating Expenses	132.7	112.5	448.5	117.0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 4.6	$ 33.6	(43.1)	272.7
Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Amortization			0.9	0.9
Jackalope Gas Gathering Services, L.L.C.
Schedule of Equity Method Investments [Line Items]
Amortization				0.1
Powder River Basin Industrial Complex, LLC
Schedule of Equity Method Investments [Line Items]
Amortization				0.3
Crestwood Niobrara LLC | Williams Partners LP
Schedule of Equity Method Investments [Line Items]
Additional voting rights acquired					50.00%
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Operating Revenues			206.5	205.1
Operating Expenses			171.9	153.2
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest			35.5	51.1
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Stagecoach Gas Services LLC
Schedule of Equity Method Investments [Line Items]
Operating Revenues			115.3	120.8
Operating Expenses			58.9	61.1
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest			56.5	60.0
Equity Method Investment, Nonconsolidated Investee or Group of Investees | Other Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Operating Revenues			91.2	84.3
Operating Expenses			113.0	92.1
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest			$ (21.0)	$ (8.9)