Fair Value Measurements - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 01, 2017 USD ($)	Oct. 02, 2016 USD ($)	Oct. 01, 2017 USD ($) segment	Oct. 02, 2016 USD ($)	Jan. 01, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on available-for-sale investments, net of tax	$ 28.8	$ 1.3	$ 48.6	$ 8.8
Number of reportable segments | segment			3
Temp Holdings Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on available-for-sale investments, net of tax	28.8	$ 1.3	$ 48.6	$ 8.8
Cost of available-for-sale investments	$ 18.4		$ 18.4		$ 17.7