Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income by Component, Net of Tax (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 01, 2017	Oct. 02, 2016	Oct. 01, 2017	Oct. 02, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 1,012.0
Other comprehensive income	$ 32.2	$ 3.3	64.6	$ 21.8
Ending balance	1,127.0	1,016.5	1,127.0	1,016.5
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(10.7)	(11.6)	(23.3)	(22.6)
Other comprehensive income before reclassifications	3.4	1.8	16.0	13.1
Amounts reclassified from accumulated other comprehensive income	0.0	0.2	0.0	(0.1)
Other comprehensive income	3.4	2.0	16.0	13.0
Ending balance	(7.3)	(9.6)	(7.3)	(9.6)
Unrealized Gains and Losses on Investment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	103.6	92.4	83.8	84.9
Other comprehensive income before reclassifications	28.8	1.3	48.6	8.8
Amounts reclassified from accumulated other comprehensive income	0.0	0.0	0.0	0.0
Other comprehensive income	28.8	1.3	48.6	8.8
Ending balance	132.4	93.7	132.4	93.7
Pension Liability Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1.8)	(1.6)	(1.8)	(1.6)
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	0.0	0.0	0.0	0.0
Ending balance	(1.8)	(1.6)	(1.8)	(1.6)
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	91.1	79.2	58.7	60.7
Other comprehensive income before reclassifications	32.2	3.1	64.6	21.9
Amounts reclassified from accumulated other comprehensive income	0.0	0.2	0.0	(0.1)
Other comprehensive income	32.2	3.3	64.6	21.8
Ending balance	$ 123.3	$ 82.5	$ 123.3	$ 82.5