Changes In Other Comprehensive Loss - Changes in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance Total Member's Interest	$ 2,745.3	$ 1,569.3
Other Comprehensive (Loss) Income before Reclassifications	(28.0)
Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income	45.1
Net Current-period Other Comprehensive Income (Loss)	17.1	(58.5)	$ 48.8
Ending balance Total Member's Interest	2,856.6	2,745.3	1,569.3
Derivatives Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance Total Member's Interest	(11.9)
Other Comprehensive (Loss) Income before Reclassifications	(7.2)
Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income	(1.7)
Net Current-period Other Comprehensive Income (Loss)	(8.9)
Ending balance Total Member's Interest	(20.8)	(11.9)
Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance Total Member's Interest	(259.1)
Other Comprehensive (Loss) Income before Reclassifications	(33.2)
Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income	46.8
Net Current-period Other Comprehensive Income (Loss)	13.6	(32.4)	8.8
Ending balance Total Member's Interest	(245.5)	(259.1)
Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance Total Member's Interest	(126.3)
Other Comprehensive (Loss) Income before Reclassifications	12.4
Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income	0.0
Net Current-period Other Comprehensive Income (Loss)	12.4	(24.5)	$ 44.9
Ending balance Total Member's Interest	(113.9)	(126.3)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance Total Member's Interest	(397.3)
Ending balance Total Member's Interest	$ (380.2)	$ (397.3)