Segment Information Revenues and Operating Margin (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Sales of commodities									$ 5,626.8	$ 5,465.4	$ 7,595.2
Fees from midstream services									1,064.1	1,193.2	1,021.3
Revenues	$ 2,012.6	$ 1,652.3	$ 1,583.6	$ 1,442.4	$ 1,647.4	$ 1,632.1	$ 1,699.4	$ 1,679.7	6,690.9	6,658.6	8,616.5
Operating margin									1,214.3	1,281.0	1,136.5
Gathering and Processing [Member]
Revenues
Revenues									3,240.7	3,047.5	2,851.1
Operating margin									577.1	515.1	449.9
Logistics and Marketing [Member]
Revenues
Revenues									5,794.5	4,888.6	8,215.2
Operating margin									574.4	681.7	694.7
Other Segment [Member]
Revenues
Revenues									62.9	84.2	(8.0)
Operating margin									62.9	84.2	(8.0)
Splitter Agreement [Member]
Revenues
Revenues									(2,407.2)	(1,361.7)	(2,441.8)
Operating margin									(0.1)		(0.1)
Operating Segments [Member]
Revenues
Sales of commodities									5,626.8	5,465.4	7,595.2
Fees from midstream services									1,064.1	1,193.2	1,021.3
Revenues									6,690.9	6,658.6	8,616.5
Operating Segments [Member] | Gathering and Processing [Member]
Revenues
Sales of commodities									621.9	1,485.4	552.4
Fees from midstream services									486.6	427.1	224.7
Revenues									1,108.5	1,912.5	777.1
Operating Segments [Member] | Logistics and Marketing [Member]
Revenues
Sales of commodities									4,942.0	3,895.8	7,050.8
Fees from midstream services									577.5	766.1	796.6
Revenues									5,519.5	4,661.9	7,847.4
Operating Segments [Member] | Other Segment [Member]
Revenues
Sales of commodities									62.9	84.2	(8.0)
Revenues									62.9	84.2	(8.0)
Intersegment Eliminations [Member] | Gathering and Processing [Member]
Revenues
Sales of commodities									2,124.4	1,126.3	2,068.8
Fees from midstream services									7.8	8.7	5.2
Revenues									2,132.2	1,135.0	2,074.0
Intersegment Eliminations [Member] | Logistics and Marketing [Member]
Revenues
Sales of commodities									251.5	208.9	339.3
Fees from midstream services									23.5	17.8	28.5
Revenues									275.0	226.7	367.8
Intersegment Eliminations [Member] | Splitter Agreement [Member]
Revenues
Sales of commodities									(2,375.9)	(1,335.2)	(2,408.1)
Fees from midstream services									(31.3)	(26.5)	(33.7)
Revenues									$ (2,407.2)	$ (1,361.7)	$ (2,441.8)