Segment Information - Revenues and Operating Margin (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Revenues	$ 8,260.3	$ 8,671.1	$ 10,484.0
Operating margin	2,375.4	1,759.7	1,523.8
Sales of Commodities [Member]
Revenues:
Revenues	7,171.0	7,393.8	9,278.7
Fees from Midstream Services [Member]
Revenues:
Revenues	1,089.3	1,277.3	1,205.3
Gathering and Processing [Member]
Revenues:
Revenues	3,326.8	4,465.4	5,587.0
Operating margin	1,017.7	1,006.4	939.2
Logistics and Transportation [Member]
Revenues:
Revenues	7,120.9	7,116.3	8,896.0
Operating margin	1,128.0	867.2	592.5
Other [Member]
Revenues:
Revenues	229.7	(113.9)	(7.9)
Operating margin	229.7	(113.9)	(7.9)
Corporate and Eliminations [Member]
Revenues:
Revenues	(2,417.1)	(2,796.7)	(3,991.1)
Operating Segments [Member]
Revenues:
Revenues	8,260.3	8,671.1	10,484.0
Operating Segments [Member] \| Sales of Commodities [Member]
Revenues:
Revenues	7,171.0	7,393.8	9,278.7
Operating Segments [Member] \| Fees from Midstream Services [Member]
Revenues:
Revenues	1,089.3	1,277.3	1,205.3
Operating Segments [Member] \| Gathering and Processing [Member]
Revenues:
Revenues	1,147.1	1,829.6	1,943.8
Operating Segments [Member] \| Gathering and Processing [Member] \| Sales of Commodities [Member]
Revenues:
Revenues	659.9	1,101.6	1,228.2
Operating Segments [Member] \| Gathering and Processing [Member] \| Fees from Midstream Services [Member]
Revenues:
Revenues	487.2	728.0	715.6
Operating Segments [Member] \| Logistics and Transportation [Member]
Revenues:
Revenues	6,883.5	6,955.4	8,548.1
Operating Segments [Member] \| Logistics and Transportation [Member] \| Sales of Commodities [Member]
Revenues:
Revenues	6,281.4	6,406.1	8,058.4
Operating Segments [Member] \| Logistics and Transportation [Member] \| Fees from Midstream Services [Member]
Revenues:
Revenues	602.1	549.3	489.7
Operating Segments [Member] \| Other [Member]
Revenues:
Revenues	229.7	(113.9)	(7.9)
Operating Segments [Member] \| Other [Member] \| Sales of Commodities [Member]
Revenues:
Revenues	229.7	(113.9)	(7.9)
Intersegment Eliminations [Member] \| Gathering and Processing [Member]
Revenues:
Revenues	2,179.7	2,635.8	3,643.2
Intersegment Eliminations [Member] \| Gathering and Processing [Member] \| Sales of Commodities [Member]
Revenues:
Revenues	2,173.2	2,628.4	3,636.0
Intersegment Eliminations [Member] \| Gathering and Processing [Member] \| Fees from Midstream Services [Member]
Revenues:
Revenues	6.5	7.4	7.2
Intersegment Eliminations [Member] \| Logistics and Transportation [Member]
Revenues:
Revenues	237.4	160.9	347.9
Intersegment Eliminations [Member] \| Logistics and Transportation [Member] \| Sales of Commodities [Member]
Revenues:
Revenues	205.9	132.2	317.1
Intersegment Eliminations [Member] \| Logistics and Transportation [Member] \| Fees from Midstream Services [Member]
Revenues:
Revenues	31.5	28.7	30.8
Intersegment Eliminations [Member] \| Corporate and Eliminations [Member]
Revenues:
Revenues	(2,417.1)	(2,796.7)	(3,991.1)
Intersegment Eliminations [Member] \| Corporate and Eliminations [Member] \| Sales of Commodities [Member]
Revenues:
Revenues	(2,379.1)	(2,760.6)	(3,953.1)
Intersegment Eliminations [Member] \| Corporate and Eliminations [Member] \| Fees from Midstream Services [Member]
Revenues:
Revenues	$ (38.0)	$ (36.1)	$ (38.0)