Condensed Consolidating Financial Statements (Schedule of Condensed Consolidating Statements of Comprehensive Operations) (Details) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 27, 2019		Sep. 27, 2019		Jun. 28, 2019		Mar. 29, 2019		Dec. 28, 2018		Sep. 28, 2018		Jun. 29, 2018		Mar. 30, 2018		Dec. 27, 2019	Dec. 28, 2018	Dec. 29, 2017
Condensed Consolidating Financial Statements
Net sales	$ 804.9		$ 743.7		$ 823.3		$ 790.6		$ 834.9		$ 799.9		$ 825.5		$ 755.3		$ 3,162.5	$ 3,215.6	$ 3,221.6
Cost of sales																	1,741.1	1,744.4	1,564.1
Gross profit	373.1		324.3		388.9		335.1		363.3		366.4		394.0		347.5		1,421.4	1,471.2	1,657.5
Selling, general and administrative expenses																	831.0	834.1	849.7
Research and development expenses																	349.4	361.1	276.9
Restructuring charges, net																	(1.7)	103.0	31.2
Non-restructuring impairment charges																	388.0	3,893.1	63.7
Losses (gains) on divestiture																	33.5	(0.8)
Opioid-related litigation settlement charge																	1,643.4	0.0	0.0
Operating income (loss)																	(1,822.2)	(3,720.9)	492.9
Interest expense																	(309.0)	(370.2)	(369.1)
Interest income																	9.5	8.2	4.6
Gains on debt extinguishment, net	377.4																466.6	8.5	8.3
Other income (expense), net																	63.6	22.4	(75.1)
Intercompany interest and fees																	0.0	0.0	0.0
Equity in net income of subsidiaries																	0.0	0.0	0.0
Income (loss) from continuing operations before income taxes																	(1,591.5)	(4,052.0)	61.6
Income Tax Expense (Benefit)																	(584.3)	(430.1)	(1,709.6)
Income (loss) from continuing operations	(1,161.0)	[1]	(0.9)	[1]	(0.5)	[1]	155.2	[1]	(3,718.4)	[2],[3]	114.2	[2],[3]	3.2	[2],[3]	(20.9)	[2],[3]	(1,007.2)	(3,621.9)	1,771.2
Income (loss) from discontinued operations, net of income taxes	3.9		(0.2)		7.3		(0.3)		0.0		(0.4)		12.4		2.9		10.7	14.9	363.2
Net income (loss)	$ (1,157.1)		$ (1.1)		$ 6.8		$ 154.9		$ (3,718.4)		$ 113.8		$ 15.6		$ (18.0)		(996.5)	(3,607.0)	2,134.4
Other comprehensive loss, net of tax																	15.9	(9.9)	59.6
Comprehensive income (loss)																	(980.6)	(3,616.9)	2,194.0
Mallinckrodt plc
Condensed Consolidating Financial Statements
Net sales																	0.0	0.0	0.0
Cost of sales																	1.9	2.0	2.6
Gross profit																	(1.9)	(2.0)	(2.6)
Selling, general and administrative expenses																	43.9	38.8	59.5
Research and development expenses																	5.2	4.7	5.1
Restructuring charges, net																	0.0	0.0	0.0
Non-restructuring impairment charges																	0.0	0.0	0.0
Losses (gains) on divestiture																	4.2	0.0
Opioid-related litigation settlement charge																	43.4
Operating income (loss)																	(98.6)	(45.5)	(67.2)
Interest expense																	(5.8)	(7.8)	13.8
Interest income																	9.8	9.5	7.3
Gains on debt extinguishment, net																	0.0	0.0	0.0
Other income (expense), net																	9.2	9.9	20.3
Intercompany interest and fees																	20.4	18.5	18.3
Equity in net income of subsidiaries																	(895.8)	(3,561.0)	2,200.0
Income (loss) from continuing operations before income taxes																	(1,001.6)	(3,613.4)	2,128.3
Income Tax Expense (Benefit)																	(5.1)	(6.4)	(6.1)
Income (loss) from continuing operations																	(996.5)	(3,607.0)	2,134.4
Income (loss) from discontinued operations, net of income taxes																	0.0	0.0	0.0
Net income (loss)																	(996.5)	(3,607.0)	2,134.4
Other comprehensive loss, net of tax																	15.9	(9.9)	59.6
Comprehensive income (loss)																	(980.6)	(3,616.9)	2,194.0
Mallinckrodt International Finance S.A.
Condensed Consolidating Financial Statements
Net sales																	0.0	0.0	0.0
Cost of sales																	0.0	0.0	0.0
Gross profit																	0.0	0.0	0.0
Selling, general and administrative expenses																	1.6	0.7	0.7
Research and development expenses																	0.0	0.0	0.0
Restructuring charges, net																	0.0	0.0	0.0
Non-restructuring impairment charges																	0.0	0.0	0.0
Losses (gains) on divestiture																	0.0	0.0
Opioid-related litigation settlement charge																	0.0
Operating income (loss)																	(1.6)	(0.7)	(0.7)
Interest expense																	(282.1)	(460.8)	(353.9)
Interest income																	1.3	2.5	1.2
Gains on debt extinguishment, net																	420.9	8.5	8.3
Other income (expense), net																	0.0	0.2	(10.0)
Intercompany interest and fees																	0.1	0.1	0.0
Equity in net income of subsidiaries																	(933.4)	(2,726.0)	2,901.8
Income (loss) from continuing operations before income taxes																	(795.0)	(3,176.4)	2,546.7
Income Tax Expense (Benefit)																	(2.6)	(5.4)	(5.3)
Income (loss) from continuing operations																	(792.4)	(3,171.0)	2,552.0
Income (loss) from discontinued operations, net of income taxes																	5.4	0.1	(2.1)
Net income (loss)																	(787.0)	(3,170.9)	2,549.9
Other comprehensive loss, net of tax																	15.9	(9.9)	59.6
Comprehensive income (loss)																	(771.1)	(3,180.8)	2,609.5
Other Subsidiaries
Condensed Consolidating Financial Statements
Net sales																	3,162.5	3,215.6	3,221.6
Cost of sales																	1,739.2	1,742.4	1,561.5
Gross profit																	1,423.3	1,473.2	1,660.1
Selling, general and administrative expenses																	785.5	794.6	789.5
Research and development expenses																	344.2	356.4	271.8
Restructuring charges, net																	(1.7)	103.0	31.2
Non-restructuring impairment charges																	388.0	3,893.1	63.7
Losses (gains) on divestiture																	29.3	(0.8)
Opioid-related litigation settlement charge																	1,600.0
Operating income (loss)																	(1,722.0)	(3,674.7)	560.8
Interest expense																	(235.9)	(63.4)	(74.2)
Interest income																	213.2	158.0	68.9
Gains on debt extinguishment, net																	45.7	0.0	0.0
Other income (expense), net																	54.4	12.3	(85.4)
Intercompany interest and fees																	(20.5)	(18.6)	(18.3)
Equity in net income of subsidiaries																	(787.0)	(3,170.9)	2,549.9
Income (loss) from continuing operations before income taxes																	(2,411.1)	(6,720.1)	3,038.3
Income Tax Expense (Benefit)																	(576.6)	(418.3)	(1,698.2)
Income (loss) from continuing operations																	(1,834.5)	(6,301.8)	4,736.5
Income (loss) from discontinued operations, net of income taxes																	5.3	14.8	365.3
Net income (loss)																	(1,829.2)	(6,287.0)	5,101.8
Other comprehensive loss, net of tax																	30.0	(20.5)	118.2
Comprehensive income (loss)																	(1,799.2)	(6,307.5)	5,220.0
Eliminations
Condensed Consolidating Financial Statements
Net sales																	0.0	0.0	0.0
Cost of sales																	0.0	0.0	0.0
Gross profit																	0.0	0.0	0.0
Selling, general and administrative expenses																	0.0	0.0	0.0
Research and development expenses																	0.0	0.0	0.0
Restructuring charges, net																	0.0	0.0	0.0
Non-restructuring impairment charges																	0.0	0.0	0.0
Losses (gains) on divestiture																	0.0	0.0
Opioid-related litigation settlement charge																	0.0
Operating income (loss)																	0.0	0.0	0.0
Interest expense																	214.8	161.8	72.8
Interest income																	(214.8)	(161.8)	(72.8)
Gains on debt extinguishment, net																	0.0	0.0	0.0
Other income (expense), net																	0.0	0.0	0.0
Intercompany interest and fees																	0.0	0.0	0.0
Equity in net income of subsidiaries																	2,616.2	9,457.9	(7,651.7)
Income (loss) from continuing operations before income taxes																	2,616.2	9,457.9	(7,651.7)
Income Tax Expense (Benefit)																	0.0	0.0	0.0
Income (loss) from continuing operations																	2,616.2	9,457.9	(7,651.7)
Income (loss) from discontinued operations, net of income taxes																	0.0	0.0	0.0
Net income (loss)																	2,616.2	9,457.9	(7,651.7)
Other comprehensive loss, net of tax																	(45.9)	30.4	(177.8)
Comprehensive income (loss)																	$ 2,570.3	$ 9,488.3	$ (7,829.5)

[1] Includes administration expenses and certain compensation, legal, environmental and other costs not charged to the Company's reportable segments.

[2] Loss from continuing operations for the quarter ended December 28, 2018 reflects impairment charges for goodwill and an IPR&D asset. See Note 13 for further information.

[3] The "Specialty Generics Disposal Group" was included within discontinued operations during the first three quarters of fiscal 2018, and was subsequently recast to be included within continuing operations during the fourth quarter of fiscal 2018. In accordance with U.S. GAAP, depreciation and amortization are not recorded during the period in which a disposal group is classified as held-for-sale, thus the Company's financial results during the first three quarters of fiscal 2018 did not include $17.7 million and $6.8 million of depreciation and amortization expense, respectively, related to the Specialty Generics Disposal Group. During the fourth quarter of fiscal 2018, the Specialty Generics Disposal Group was reclassified to held and used and measured at its carrying amount before it was classified as held-for-sale, adjusted for depreciation and amortization expense that would have been recognized had the disposal group been continuously classified as held and used. The total adjustment of $24.5 million was reflected in loss from continuing operations during the fourth quarter of fiscal 2018, the period in which the held-for-sale criteria were no longer met. The Specialty Generics Disposal Group included (1) the Company's Specialty Generics business comprised of what was the Company's Specialty Generics segment in fiscal 2017, with the exception of BioVectra; (2) certain of the Company's non-promoted brands business; and (3) the Company's post-divestiture supply agreement with the acquirer of the contrast media and delivery systems ("CMDS") business.