Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018		Jan. 01, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 740.4
Other comprehensive income (loss), net of tax		10.2	$ (11.7)
Ending balance		733.9	740.4
Cumulative-effect adjustment					$ 10.3	[1]	$ 0.3
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		(5.5)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(35.6)	(38.5)	$ (37.1)
Reclassification from AOCI, Current Period, Tax		1.4	1.5	2.1
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		4.7	4.8	3.5
Foreign currency translation adjustment		(0.1)	0.0	(0.1)
Other comprehensive income (loss), net of tax		2.4	2.9	(1.4)
Ending balance		(33.2)	(35.6)	(38.5)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI, before Reclassifications, before Tax, Attributable to Parent		(0.4)	4.4	(0.3)
Other Comprehensive Income (Loss) before Reclassifications, Tax		(0.1)	1.1	(0.1)
OCI, before Reclassifications, Net of Tax, Attributable to Parent		(0.3)	3.3	(0.2)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		0.5	0.9	0.9
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI, before Reclassifications, before Tax, Attributable to Parent		(2.5)	(6.9)	(7.3)
Other Comprehensive Income (Loss) before Reclassifications, Tax		(0.6)	(1.7)	(2.7)
OCI, before Reclassifications, Net of Tax, Attributable to Parent		(1.9)	(5.2)	(4.6)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		5.6	5.4	4.7
Accumulated Net Investment Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0.3	1.3	0.8
OCI, before Reclassifications, before Tax, Attributable to Parent		4.4	4.7	4.0
Other Comprehensive Income (Loss) before Reclassifications, Tax		1.1	1.1	1.5
OCI, before Reclassifications, Net of Tax, Attributable to Parent		3.3	3.6	2.5
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		(4.4)	(5.4)	(3.2)
Reclassification from AOCI, Current Period, Tax		(1.1)	(1.2)	(1.2)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		(3.3)	(4.2)	(2.0)
Other comprehensive income (loss), net of tax		0.0	(0.6)	0.5
Ending balance		0.3	0.3	1.3
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(13.4)	0.5	(0.2)
OCI, before Reclassifications, before Tax, Attributable to Parent		(9.5)	(21.2)	1.8
Other Comprehensive Income (Loss) before Reclassifications, Tax		2.3	5.3	(0.7)
OCI, before Reclassifications, Net of Tax, Attributable to Parent		(7.2)	(15.9)	1.1
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		19.7	2.7	(0.6)
Reclassification from AOCI, Current Period, Tax		(4.7)	(0.7)	0.2
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		15.0	2.0	(0.4)
Other comprehensive income (loss), net of tax		7.8	(13.9)	0.7
Ending balance		(5.6)	(13.4)	0.5
Accumulated Other Comprehensive Loss (Other) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(0.1)	0.0	(0.2)
Other comprehensive income (loss), net of tax		0.0	(0.1)	0.2
Ending balance		(0.1)	(0.1)	0.0
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(48.8)	(36.7)
Other comprehensive income (loss), net of tax		10.2	(11.7)
Ending balance		$ (38.6)	$ (48.8)	$ (36.7)
Cumulative-effect adjustment	[1]				(0.4)
Accounting Standards Update 2016-01 | Accumulated Net Investment Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative-effect adjustment					$ 0.4

[1] Cumulative-effect adjustment relates to our adoption of ASC 606 and ASU 2016-01 (each as defined in Note 1).