Document And Entity Information [Abstract] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 11, 2022	Jun. 25, 2021
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	001-35803
Entity Registrant Name	Mallinckrodt plc
Entity Incorporation, State or Country Code	L2
Entity Tax Identification Number	98-1088325
Entity Central Index Key	0001567892
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Address, Address Line One	College Business & Technology Park
Entity Address, Address Line Two	Cruiserath
Entity Address, Address Line Three	Blanchardstown
Entity Address, City or Town	Dublin
Entity Address, Postal Zip Code	15
Entity Address, Country	IE
Country Region	353
City Area Code	1
Local Phone Number	696 0000
Title of 12(b) Security	Ordinary shares, par value $0.20 per share
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 38.9
Share Price			$ 0.46
Entity Common Stock, Shares Outstanding		84,734,080
ICFR Auditor Attestation Flag	true
Auditor Firm ID	34
Auditor Name	DELOITTE & TOUCHE LLP
Auditor Location	St. Louis, Missouri