Restructuring and Related Charges (Schedule of Restructuring Reserves by Type of Cost) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 30, 2016	Dec. 29, 2017	Sep. 30, 2016	Sep. 25, 2015
Continuing Operations
Restructuring Reserve [Roll Forward]
Beginning Balance		$ 18.5	$ 14.8	$ 18.0	$ 34.9
Charges		3.8	36.7	36.0	37.0
Changes in estimate from continuing operations			(5.5)	(2.7)	(1.8)
Cash payments		(7.5)	(30.8)	(33.7)	(44.3)
Reclassifications	[1]		(0.3)	(1.3)	(3.0)
Currency translation					(0.6)
Ending Balance		14.8	15.5	18.5	18.0
Discontinued Operations, Held-for-sale
Restructuring Reserve [Roll Forward]
Charges, discontinued operations				2.5	4.7
Changes in estimate, discontinued operations				(0.3)	(8.9)
Acquisition programs | Continuing Operations
Restructuring Reserve [Roll Forward]
Beginning Balance		0.5	0.2	10.0	7.9
Charges		0.1	0.9	5.0	25.3
Changes in estimate from continuing operations			0.0	(1.3)	(1.5)
Cash payments		(0.4)	(0.3)	(13.2)	(21.7)
Reclassifications	[1]		0.0	0.0	0.0
Currency translation					0.0
Ending Balance		0.2	0.8	0.5	10.0
Acquisition programs | Discontinued Operations, Held-for-sale
Restructuring Reserve [Roll Forward]
Charges, discontinued operations				0.0	0.0
Changes in estimate, discontinued operations				0.0	0.0
Other programs | Continuing Operations
Restructuring Reserve [Roll Forward]
Beginning Balance		0.0	0.0	0.0	0.4
Charges		0.0	0.0	0.0	0.0
Changes in estimate from continuing operations			0.0	0.0	(0.3)
Cash payments		0.0	0.0	0.0	(0.1)
Reclassifications	[1]		0.0	0.0	0.0
Currency translation					0.0
Ending Balance		0.0	0.0	0.0	0.0
Other programs | Discontinued Operations, Held-for-sale
Restructuring Reserve [Roll Forward]
Charges, discontinued operations				0.0	0.0
Changes in estimate, discontinued operations				0.0	0.0
2016 Mallinckrodt Program | Continuing Operations
Restructuring Reserve [Roll Forward]
Beginning Balance		6.2	9.5	0.0	0.0
Charges		3.7	35.8	6.4	0.0
Changes in estimate from continuing operations			(4.8)	0.0	0.0
Cash payments		(0.4)	(26.1)	(0.2)	0.0
Reclassifications	[1]		(0.3)	0.0	0.0
Currency translation					0.0
Ending Balance		9.5	14.7	6.2	0.0
2016 Mallinckrodt Program | Discontinued Operations, Held-for-sale
Restructuring Reserve [Roll Forward]
Charges, discontinued operations				0.0	0.0
Changes in estimate, discontinued operations				0.0	0.0
2013 Mallinckrodt program | Continuing Operations
Restructuring Reserve [Roll Forward]
Beginning Balance		11.8	5.1	8.0	26.6
Charges		0.0	0.0	24.6	11.7
Changes in estimate from continuing operations			(0.7)	(1.4)	0.0
Cash payments		(6.7)	(4.4)	(20.3)	(22.5)
Reclassifications	[1]		0.0	(1.3)	(3.0)
Currency translation					(0.6)
Ending Balance		$ 5.1	$ 0.0	11.8	8.0
2013 Mallinckrodt program | Discontinued Operations, Held-for-sale
Restructuring Reserve [Roll Forward]
Charges, discontinued operations				2.5	4.7
Changes in estimate, discontinued operations				$ (0.3)	$ (8.9)

[1] Represents the reclassification of pension and other postretirement benefits from restructuring reserves to pension and postretirement obligations.