Document And Entity Information [Abstract] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 27, 2019	Feb. 21, 2020	Jun. 28, 2019
Document and Entity Information [Abstract]
Title of 12(b) Security	Ordinary shares, par value $0.20 per share
Entity Incorporation, State or Country Code	L2
Document Transition Report	false
Document Annual Report	true
Entity Common Stock, Shares Outstanding		84,207,022
Entity Registrant Name	Mallinckrodt plc
Share Price			$ 9.18
Entity Central Index Key	0001567892
Trading Symbol	MNK
Current Fiscal Year End Date	--12-27
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 27, 2019
Entity File Number	001-35803
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Public Float			$ 764.7
Entity Tax Identification Number	98-1088325
Entity Address, Address Line One	3 Lotus Park, The Causeway
Entity Address, City or Town	Staines-Upon-Thames
Entity Address, Postal Zip Code	TW18 3AG
Security Exchange Name	NYSE
Entity Address, Country	GB
City Area Code	017
Local Phone Number	8463 6700