Segment Information - Revenues and Operating Margin (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Revenues	$ 1,523.5	$ 1,995.3	$ 3,572.4	$ 4,294.7
Operating margin	479.5	423.5	1,145.5	806.6
Sales of Commodities [Member]
Revenues:
Revenues	1,280.6	1,684.2	3,060.2	3,660.7
Fees from Midstream Services [Member]
Revenues:
Revenues	242.9	311.1	512.2	634.0
Gathering and Processing [Member]
Revenues:
Revenues	634.2	1,015.8	1,441.2	2,297.0
Operating margin	237.2	232.1	492.8	470.3
Logistics and Transportation [Member]
Revenues:
Revenues	1,322.6	1,564.3	2,957.8	3,458.1
Operating margin	231.5	184.4	525.5	336.3
Other [Member]
Revenues:
Revenues	10.8	7.0	127.2
Operating margin	10.8	7.0	127.2
Corporate and Eliminations [Member]
Revenues:
Revenues	(444.1)	(591.8)	(953.8)	(1,460.4)
Operating Segments [Member]
Revenues:
Revenues	1,523.5	1,995.3	3,572.4	4,294.7
Operating Segments [Member] | Sales of Commodities [Member]
Revenues:
Revenues	1,280.6	1,684.2	3,060.2	3,660.7
Operating Segments [Member] | Fees from Midstream Services [Member]
Revenues:
Revenues	242.9	311.1	512.2	634.0
Operating Segments [Member] | Gathering and Processing [Member]
Revenues:
Revenues	243.5	474.6	605.5	931.2
Operating Segments [Member] | Gathering and Processing [Member] | Sales of Commodities [Member]
Revenues:
Revenues	133.5	298.4	377.3	555.1
Operating Segments [Member] | Gathering and Processing [Member] | Fees from Midstream Services [Member]
Revenues:
Revenues	110.0	176.2	228.2	376.1
Operating Segments [Member] | Logistics and Transportation [Member]
Revenues:
Revenues	1,269.2	1,513.7	2,839.7	3,363.5
Operating Segments [Member] | Logistics and Transportation [Member] | Sales of Commodities [Member]
Revenues:
Revenues	1,136.3	1,378.8	2,555.7	3,105.6
Operating Segments [Member] | Logistics and Transportation [Member] | Fees from Midstream Services [Member]
Revenues:
Revenues	132.9	134.9	284.0	257.9
Operating Segments [Member] | Other [Member]
Revenues:
Revenues	10.8	7.0	127.2
Operating Segments [Member] | Other [Member] | Sales of Commodities [Member]
Revenues:
Revenues	10.8	7.0	127.2
Intersegment Eliminations [Member] | Gathering and Processing [Member]
Revenues:
Revenues	390.7	541.2	835.7	1,365.8
Intersegment Eliminations [Member] | Gathering and Processing [Member] | Sales of Commodities [Member]
Revenues:
Revenues	389.2	539.7	832.4	1,362.5
Intersegment Eliminations [Member] | Gathering and Processing [Member] | Fees from Midstream Services [Member]
Revenues:
Revenues	1.5	1.5	3.3	3.3
Intersegment Eliminations [Member] | Logistics and Transportation [Member]
Revenues:
Revenues	53.4	50.6	118.1	94.6
Intersegment Eliminations [Member] | Logistics and Transportation [Member] | Sales of Commodities [Member]
Revenues:
Revenues	46.1	43.6	102.7	82.1
Intersegment Eliminations [Member] | Logistics and Transportation [Member] | Fees from Midstream Services [Member]
Revenues:
Revenues	7.3	7.0	15.4	12.5
Intersegment Eliminations [Member] | Corporate and Eliminations [Member]
Revenues:
Revenues	(444.1)	(591.8)	(953.8)	(1,460.4)
Intersegment Eliminations [Member] | Corporate and Eliminations [Member] | Sales of Commodities [Member]
Revenues:
Revenues	(435.3)	(583.3)	(935.1)	(1,444.6)
Intersegment Eliminations [Member] | Corporate and Eliminations [Member] | Fees from Midstream Services [Member]
Revenues:
Revenues	$ (8.8)	$ (8.5)	$ (18.7)	$ (15.8)