Recently Issued Accounting Standards (Details) - USD ($) $ in Millions	Jun. 28, 2019	Dec. 29, 2018
Operating Lease, Right-of-Use Asset	$ 90.6
Operating Lease, Liability	$ 97.3
Accounting Standards Update 2018-02 [Member] \| Retained Earnings (Deficit)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets		$ 0.5
Accounting Standards Update 2016-02 [Member]
Operating Lease, Right-of-Use Asset		83.1
Operating Lease, Liability		$ 99.7

Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22580-107794

+ Details

Name:	us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleCumulativeEffectOfChangeOnEquityOrNetAssets1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

Name:	us-gaap_OperatingLeaseLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

Name:	us-gaap_OperatingLeaseRightOfUseAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=mnk_AccountingStandardsUpdate201802Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_RetainedEarningsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201602Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: