Supplemental Balance Sheet Data - AOCI (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period	$ 409.8	$ 406.3	$ 394.2	$ 390.2	$ 406.3	$ 390.2
Other comprehensive loss before reclassifications					(0.4)
Amounts reclassified from AOCI					3.1
Income (loss) from other comprehensive income items	5.1		7.8		2.7	6.3
Provision (benefit) for income taxes	0.4		1.6		0.6	1.8
Other comprehensive income (loss)	4.7	(2.6)	6.2	(1.7)	2.1	4.5
Balance at the end of the period	358.0	409.8	406.5	394.2	358.0	406.5
Income tax benefit	11.4		(3.2)		7.1	(5.6)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from AOCI					3.1	(3.1)
Income tax benefit					0.8	(0.8)
Net Unrealized Foreign Currency Translation Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period		(19.0)			(19.0)
Other comprehensive loss before reclassifications					(0.4)
Amounts reclassified from AOCI					0.0
Income (loss) from other comprehensive income items					(0.4)
Provision (benefit) for income taxes					(0.2)
Other comprehensive income (loss)					(0.2)
Balance at the end of the period	(19.2)				(19.2)
Net Loss from Pension and Other Postretirement Liabilities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period		(94.3)			(94.3)
Other comprehensive loss before reclassifications					0.0
Amounts reclassified from AOCI					3.1
Income (loss) from other comprehensive income items					3.1
Provision (benefit) for income taxes					0.8
Other comprehensive income (loss)					2.3
Balance at the end of the period	(92.0)				(92.0)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at the beginning of the period	(115.9)	(113.3)	(106.8)	(105.1)	(113.3)	(105.1)
Other comprehensive income (loss)	4.7	(2.6)	6.2	(1.7)
Balance at the end of the period	$ (111.2)	$ (115.9)	$ (100.6)	$ (106.8)	$ (111.2)	$ (100.6)