Members' Equity - Computation and Distribution Activity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Distributed earnings allocated to:
Total distributed earnings	$ 46.6		$ 110.6
Undistributed loss allocated to:
Total undistributed loss	(333.4)		(286.9)
Net loss allocated to:
Total net loss	$ (286.8)		$ (176.3)
Basic and diluted net loss per unit:
Basic (in dollars per share)	$ (0.59)		$ (0.45)
Diluted (in dollars per share)	(0.59)		(0.45)
Distribution declared/unit (in dollars per share)	0.09375	$ 0.1875	0.279	$ 0.275
Distribution paid per unit (in dollars per share)	$ 0.279		$ 0.279
Unvested restricted units
Distributed earnings allocated to:
Total distributed earnings	$ 0.8		$ 1.2
Undistributed loss allocated to:
Total undistributed loss	(6.0)		(3.1)
Net loss allocated to:
Total net loss	(5.2)		(1.9)
Common units
Distributed earnings allocated to:
Total distributed earnings	45.8		109.4
Undistributed loss allocated to:
Total undistributed loss	(327.4)		(283.8)
Net loss allocated to:
Total net loss	$ (281.6)		$ (174.4)