Non-debtor Entity Intercompany Balances (Details) - USD ($) $ in Millions	Mar. 26, 2021	Dec. 25, 2020
Schedule of Non-debtor Entity Intercompany Balances [Line Items]
Non-Debtor Intercompany Receivables From Debtor Entities	$ 135.4	$ 282.3
Non-Debtor Intercompany Payables to Debtor Entities	$ 129.5	$ 120.3

Schedule of Non-debtor Entity Intercompany Balances [Line Items]

No definition available.

Name:	mnk_ScheduleOfNonDebtorEntityIntercompanyBalancesLineItems
Namespace Prefix:	mnk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration