Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income by Component, Net of Tax (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 1,151.5
Other comprehensive income (loss)	$ (7.0)	$ 32.2	(7.8)	$ 64.6
Ending balance	1,185.8	1,127.0	1,185.8	1,127.0
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7.7)	(10.7)	(6.9)	(23.3)
Other comprehensive income before reclassifications	(7.0)	3.4	(7.8)	16.0
Amounts reclassified from accumulated other comprehensive income	0.0	0.0	0.0	0.0
Other comprehensive income (loss)	(7.0)	3.4	(7.8)	16.0
Ending balance	(14.7)	(7.3)	(14.7)	(7.3)
Unrealized Gains and Losses on Investment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.0	103.6	140.0	83.8
Other comprehensive income before reclassifications	0.0	28.8	0.0	48.6
Amounts reclassified from accumulated other comprehensive income	0.0	0.0	0.0	0.0
Other comprehensive income (loss)	0.0	28.8	(140.0)	48.6
Ending balance	0.0	132.4	0.0	132.4
Pension Liability Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2.3)	(1.8)	(2.3)	(1.8)
Other comprehensive income before reclassifications	0.0	0.0	0.0	0.0
Amounts reclassified from accumulated other comprehensive income	0.0	0.0	0.0	0.0
Other comprehensive income (loss)	0.0	0.0	0.0	0.0
Ending balance	(2.3)	(1.8)	(2.3)	(1.8)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(10.0)	91.1	130.8	58.7
Other comprehensive income (loss)	(7.0)	32.2	(7.8)	64.6
Ending balance	(17.0)	$ 123.3	(17.0)	$ 123.3
Accounting Standards Update 2016-01 \| Unrealized Gains and Losses on Investment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustment					$ (140.0)
Accounting Standards Update 2016-01 \| Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustment	$ (140.0)		$ (140.0)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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