Supplemental Equity and Comprehensive Income Information - Changes in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019	Dec. 26, 2020
Changes in Accumulated other comprehensive loss (net of tax)
Balance at beginning of the period			$ (348.1)	$ (682.0)	$ (348.1)
Other comprehensive income (loss) before reclassifications, net of tax			(47.8)	18.0
Reclassifications to net income, net of tax			2.0	264.7
Net current-period other comprehensive income (loss), net of tax	$ 9.3	$ (29.5)	(45.8)	282.7
Balance at end of the period	(393.9)	(399.3)	(393.9)	(399.3)
ADPP
Changes in Accumulated other comprehensive loss (net of tax)
Reclassifications to net income, net of tax					179.3
Foreign Currency Translation
Changes in Accumulated other comprehensive loss (net of tax)
Balance at beginning of the period			(245.1)	(247.4)	(245.1)
Other comprehensive income (loss) before reclassifications, net of tax			(45.5)	(17.1)
Net current-period other comprehensive income (loss), net of tax			(45.5)	(17.1)
Balance at end of the period	(290.6)	(264.5)	(290.6)	(264.5)
Pension and Other Postretirement Benefits
Changes in Accumulated other comprehensive loss (net of tax)
Balance at beginning of the period			(101.8)	(434.3)	(101.8)
Other comprehensive income (loss) before reclassifications, net of tax				36.0
Reclassifications to net income, net of tax			1.9	265.4
Net current-period other comprehensive income (loss), net of tax			1.9	301.4
Balance at end of the period	(99.9)	(132.9)	(99.9)	(132.9)
Pension and Other Postretirement Benefits | ADPP
Changes in Accumulated other comprehensive loss (net of tax)
Other comprehensive income (loss) before reclassifications, net of tax					10.7
Reclassifications to net income, net of tax					444.7
Cash Flow Hedges
Changes in Accumulated other comprehensive loss (net of tax)
Balance at beginning of the period			(1.2)	(0.3)	$ (1.2)
Other comprehensive income (loss) before reclassifications, net of tax			(2.3)	(0.9)
Reclassifications to net income, net of tax			0.1	(0.7)
Net current-period other comprehensive income (loss), net of tax			(2.2)	(1.6)
Balance at end of the period	$ (3.4)	$ (1.9)	$ (3.4)	$ (1.9)