Business Combinations, Purchase Price Allocation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Mar. 29, 2018
Liabilities assumed in business combination:
Goodwill	$ 5,745.2	$ 5,448.9	$ 5,745.2
Delaware Basin Gas Processing LLC [Member]
Consideration:
Purchase price for remaining 50% equity interest in Delaware Processing	154.5
Fair value of our 50% equity interest in Delaware Processing held before the acquisition	146.4
Total consideration	$ 300.9
Assets acquired in business combination:
Current assets, including cash				$ 10.8
Property, plant, and equipment				200.0
Total assets acquired				303.3
Liabilities assumed in business combination:
Current liabilities				(1.8)
Long-term liabilities				(0.6)
Total liabilities assumed				(2.4)
Total identifiable net assets				300.9
Goodwill				0.0
Description of Business Combination:
Cash acquired				3.9
Delaware Basin Gas Processing LLC [Member] | Contract-based intangibles [Member]
Assets acquired in business combination:
Intangible assets				82.6
Delaware Basin Gas Processing LLC [Member] | Customer relationship intangibles [Member]
Assets acquired in business combination:
Intangible assets				$ 9.9