| Document and Entity Information | Mar. 10, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Mar. 10, 2021 |
| Entity Registrant Name | Mallinckrodt plc |
| Entity Incorporation, State or Country Code | L2 |
| Entity File Number | 001-35803 |
| Entity Tax Identification Number | 98-1088325 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Security Exchange Name | NONE |
| Title of 12(b) Security | Ordinary shares, par value $0.20 per share |
| Entity Emerging Growth Company | false |
| No Trading Symbol Flag | true |
| Entity Central Index Key | 0001567892 |
| Amendment Flag | false |
