Other Postretirement Benefits - Other Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 25, 2016	Dec. 28, 2014	Dec. 25, 2016	Dec. 28, 2014	Dec. 27, 2015
Other Postretirement Benefits
Unrecognized prior service cost due to change in plan provisions				$ (25.5)
Unrecognized (gain)/loss due to change in discount rate				3.6
Total effect of other postretirement benefit changes				$ 21.9
Postemployment benefits liability	$ 11.4		$ 11.4		$ 12.9
Increase (decrease) in postretirement benefit obligation due to changes in mortality assumptions	$ (1.2)	$ 4.2
Decrease in service costs and interest costs			$ 1.0
Minimum [Member]
Other Postretirement Benefits
Spot rate used in calculation of service and interest costs			1.32%
Maximum [Member]
Other Postretirement Benefits
Spot rate used in calculation of service and interest costs			4.79%