Segment Information - Other Financial Information (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Other financial information [Abstract]
Total assets		$ 15,411.8		$ 15,411.8		$ 15,875.7
Operating Segments [Member]
Other financial information [Abstract]
Total assets	[1]	15,411.8	$ 15,965.4	15,411.8	$ 15,965.4
Goodwill		45.2	45.2	45.2	45.2
Capital expenditures		115.5	169.6	199.0	473.8
Operating Segments [Member] | Gathering and Processing [Member]
Other financial information [Abstract]
Total assets	[1]	8,494.2	9,124.2	8,494.2	9,124.2
Goodwill		45.2	45.2	45.2	45.2
Capital expenditures		114.0	37.1	183.5	154.6
Operating Segments [Member] | Logistics And Transportation [Member]
Other financial information [Abstract]
Total assets	[1]	6,687.2	6,697.2	6,687.2	6,697.2
Capital expenditures		14.8	127.9	25.2	306.3
Operating Segments [Member] | Other [Member]
Other financial information [Abstract]
Total assets	[1]	46.8	22.0	46.8	22.0
Operating Segments [Member] | Corporate and Eliminations [Member]
Other financial information [Abstract]
Total assets	[1]	183.6	122.0	183.6	122.0
Capital expenditures		$ (13.3)	$ 4.6	$ (9.7)	$ 12.9

[1] Assets in the Corporate and Eliminations column primarily include tax-related assets, cash, prepaids and debt issuance costs for our revolving credit facilities.