Segments (Reconciliation of Net Income (Loss) to EBITDA) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net income (loss)	$ 319.9	$ 67.0	$ (166.6)
Interest and debt expense, net	(115.4)	(99.2)	(99.4)
Loss on modification/extinguishment of debt	0.0	0.9	37.7
(Provision) benefit for income taxes	0.3	0.1	(0.8)
Depreciation, amortization and accretion	195.8	168.7	191.7
EBITDA	631.4	335.9	161.4
CMLP
Segment Reporting Information [Line Items]
Net income (loss)	310.6	58.6	(175.5)
Interest and debt expense, net	(115.4)	(99.2)	(99.4)
Loss on modification/extinguishment of debt	0.0	0.9	37.7
(Provision) benefit for income taxes	0.3	0.0	0.0
Depreciation, amortization and accretion	209.9	181.4	202.7
EBITDA	$ 636.2	$ 340.1	$ 164.3