Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 27, 2015	Sep. 28, 2014	Sep. 27, 2015	Sep. 28, 2014	Dec. 28, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on available-for-sale investments, net of tax	$ 16.4	$ (1.9)	$ 23.0	$ 8.6
Cost of available-for-sale investments	17.2		17.2		$ 17.2
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	$ 16.4	$ (1.9)	$ 23.0	$ 8.6