Investments in Unconsolidated Affiliates (Distributions and Contributions) (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments		$ 57.6	$ 55.2
Payments to acquire equity method investments		6.0	52.3
Stagecoach Gas Services LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments		44.5	37.2
Payments to acquire equity method investments		0.0	0.0
Jackalope Gas Gathering Services, L.L.C.
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments		0.0	11.6
Payments to acquire equity method investments		0.0	24.4
Crestwood Permian Basin Holdings LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments		8.5	2.9
Payments to acquire equity method investments		0.0	21.4
Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments		4.4	3.5
Payments to acquire equity method investments		6.0	6.3
Powder River Basin Industrial Complex, LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments		0.2	0.0
Payments to acquire equity method investments		$ 0.0	$ 0.2
Subsequent Event | Stagecoach Gas Services LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments	$ 15.3
Subsequent Event | Crestwood Permian Basin Holdings LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments	3.4
Subsequent Event | Tres Palacios Holdings LLC
Schedule of Equity Method Investments [Line Items]
Proceeds from equity method investments	$ 2.0