Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018		Jan. 01, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative-effect adjustment			$ 0.3		$ 10.3	[1]	$ 0.7
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		$ (15.6)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		746.3
Other comprehensive income (loss), net of tax		(11.7)		$ (5.0)
Ending balance		740.4	746.3
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(38.5)	(37.1)	(31.3)
Reclassification from AOCI, Current Period, Tax		1.5	2.1	1.7
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		4.8	3.5	2.9
Defined Benefit Plan, Benefit Obligation, Foreign Currency Translation Gain (Loss)		0.0	(0.1)	0.1
Other comprehensive income (loss), net of tax		2.9	(1.4)	(5.8)
Ending balance		(35.6)	(38.5)	(37.1)
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		4.4	(0.3)	(5.7)
Other Comprehensive Income (Loss) before Reclassifications, Tax		1.1	(0.1)	(2.1)
OCI, before Reclassifications, Net of Tax, Attributable to Parent		3.3	(0.2)	(3.6)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		0.9	0.9	0.5
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		(6.9)	(7.3)	(8.3)
Other Comprehensive Income (Loss) before Reclassifications, Tax		(1.7)	(2.7)	(3.1)
OCI, before Reclassifications, Net of Tax, Attributable to Parent		(5.2)	(4.6)	(5.2)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		5.4	4.7	4.1
Accumulated Net Investment Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		1.3	0.8	(0.1)
OCI, before Reclassifications, before Tax, Attributable to Parent		4.7	4.0	1.9
Other Comprehensive Income (Loss) before Reclassifications, Tax		1.1	1.5	0.7
OCI, before Reclassifications, Net of Tax, Attributable to Parent		3.6	2.5	1.2
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		(5.4)	(3.2)	(0.5)
Reclassification from AOCI, Current Period, Tax		(1.2)	(1.2)	(0.2)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		(4.2)	(2.0)	(0.3)
Other comprehensive income (loss), net of tax		(0.6)	0.5	0.9
Ending balance		0.3	1.3	0.8
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0.5	(0.2)	(0.2)
OCI, before Reclassifications, before Tax, Attributable to Parent		(21.2)	1.8	(0.1)
Other Comprehensive Income (Loss) before Reclassifications, Tax		(5.3)	0.7	0.0
OCI, before Reclassifications, Net of Tax, Attributable to Parent		(15.9)	1.1	(0.1)
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent		2.7	(0.6)	0.1
Reclassification from AOCI, Current Period, Tax		0.7	(0.2)	0.0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		2.0	(0.4)	0.1
Other comprehensive income (loss), net of tax		(13.9)	0.7	0.0
Ending balance		(13.4)	0.5	(0.2)
Accumulated Other Comprehensive Loss (Other) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0.0	(0.2)	(0.1)
Other comprehensive income (loss), net of tax		(0.1)	0.2	(0.1)
Ending balance		(0.1)	0.0	(0.2)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative-effect adjustment	[1]				(0.4)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(36.7)	(36.7)
Other comprehensive income (loss), net of tax		(11.7)		(5.0)
Ending balance		$ (48.8)	$ (36.7)	$ (36.7)
Accounting Standards Update 2016-01 | Accumulated Net Investment Gain (Loss) Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative-effect adjustment					$ 0.4

[1] See Note 1 for discussion of our adoption of ASC 606 and ASU 2016-01 (as defined in Note 1).