Segments (Reconciliation of Net Income (Loss) to EBITDA) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net loss		$ (192.1)	$ (2,303.7)	$ (10.4)
Interest and debt expense, net		(125.1)	(140.1)	(127.1)
(Gain) loss on modification/extinguishment of debt	$ (10.0)	(10.0)	20.0	0.0
(Provision) benefit for income taxes		0.3	(1.4)	1.1
Depreciation, amortization and accretion		229.6	300.1	285.3
EBITDA		152.9	(1,844.9)	403.1
CMLP
Segment Reporting Information [Line Items]
Net loss		(197.5)	(1,410.6)	14.7
Interest and debt expense, net		(125.1)	(130.5)	(111.4)
(Gain) loss on modification/extinguishment of debt		(10.0)	18.9	0.0
(Provision) benefit for income taxes		0.0	0.0	0.9
Depreciation, amortization and accretion		240.5	278.5	255.4
EBITDA		$ 158.1	$ (982.7)	$ 382.4