Condensed Consolidating and Combining Financial Statements (Schedule of Condensed Consolidating and Combining Statements of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 30, 2016	Dec. 25, 2015	Dec. 29, 2017	Sep. 30, 2016	Sep. 25, 2015	Sep. 26, 2014
Condensed Consolidating Financial Statements
Restricted Cash and Investments, Current	$ 0.1	$ 47.5	$ 0.0	$ 0.1	$ 47.7
Cash Flows From Operating Activities:
Net cash (used in) provided by operating activities	195.6	311.4	727.3	1,184.6	930.5
Cash Flows From Investing Activities:
Capital expenditures	(65.2)	(49.0)	(186.1)	(182.9)	(148.0)
Acquisitions and intangibles, net of cash acquired	(1.8)	0.0	(76.3)	(245.4)	(2,154.7)
Proceeds from Divestiture of Businesses, Net of Cash Divested	0.0	263.7	576.9	266.7	0.0
Intercompany Loan Investment	0.0		0.0	0.0	0.0
Subsidiary dividend proceeds	0.0		0.0		0.0
Investment in subsidiary	0.0		0.0	0.0	0.0
Proceeds from Divestiture of Subsidiary			0.0	0.0
Payments to Acquire Subsidiary			0.0	0.0
Restricted cash			0.0
Other	(10.2)	(0.7)	3.9	6.0	3.0
Net cash from investing activities	(77.2)	215.4	318.4	(155.6)	(2,299.7)
Cash Flows From Financing Activities:
Issuance of external debt	190.0	62.0	1,465.0	98.3	3,010.0
Repayment of capital leases	(86.7)	(129.6)	(917.2)	(568.6)	(1,848.4)
Debt financing costs	0.0	(0.1)	(12.7)	(0.1)	(39.9)
Proceeds from exercise of share options	0.4	3.6	4.1	14.0	34.4
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	0.0				0.0
Intercompany loan borrowings	0.0		0.0	0.0	0.0
Capital contribution	0.0		0.0	0.0	0.0
Repurchase of shares	(158.8)	(275.4)	(651.7)	(652.9)	(92.2)
Other	1.2	(30.0)	(17.7)	(53.0)	(28.1)
Net cash provided by financing activities	(53.9)	(369.5)	(130.2)	(1,162.3)	1,035.8
Effect of currency rate changes on cash	(3.0)	(1.5)	2.5	0.3	(11.6)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	61.5	155.8	918.0	(133.0)	(345.0)
Cash and cash equivalents	342.0	521.9	1,260.9	280.5	365.9
Restricted Cash and Investments, Noncurrent	19.0	19.0	18.2	19.0	19.0
Cash and Cash Equivalents, Including Restricted Cash	361.1	$ 588.4	1,279.1	299.6	432.6	$ 777.6
Mallinckrodt plc
Condensed Consolidating Financial Statements
Net Cash Provided by (Used in) Operating Activities	17.4
Restricted Cash and Investments, Current	0.0		0.0	0.0	0.0
Cash Flows From Operating Activities:
Net cash (used in) provided by operating activities			1,233.2	17.9	207.0
Cash Flows From Investing Activities:
Capital expenditures	0.0		0.0	0.0	0.0
Acquisitions and intangibles, net of cash acquired	0.0		0.0	0.0	0.0
Proceeds from Divestiture of Businesses, Net of Cash Divested			0.0	0.0
Intercompany Loan Investment	0.0		(589.5)	0.0	(149.4)
Subsidiary dividend proceeds	0.0		0.0		0.0
Investment in subsidiary	0.0		0.0	0.0	0.0
Proceeds from Divestiture of Subsidiary			0.0	3.4
Payments to Acquire Subsidiary			0.0	0.0
Restricted cash			0.0
Other	0.0		0.0	0.0	0.0
Net cash from investing activities	0.0		(589.5)	3.4	(149.4)
Cash Flows From Financing Activities:
Issuance of external debt	0.0		0.0	0.0	0.0
Repayment of capital leases	0.0		0.0	0.0	0.0
Debt financing costs	0.0		0.0	0.0	0.0
Proceeds from exercise of share options	0.4		4.1	14.0	34.4
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	0.0				0.0
Intercompany loan borrowings	(140.0)		0.0	(617.8)	0.0
Capital contribution	0.0		0.0	0.0	0.0
Repurchase of shares	158.8		651.7	652.9	(92.2)
Other	1.2		4.1	0.0	0.0
Net cash provided by financing activities	(17.2)		(643.5)	(21.1)	(57.8)
Effect of currency rate changes on cash	0.0		0.0	0.0	0.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	0.2		0.2	0.2	(0.2)
Cash and cash equivalents	0.5		0.7	0.3	0.1
Restricted Cash and Investments, Noncurrent	0.0		0.0	0.0	0.0
Cash and Cash Equivalents, Including Restricted Cash	0.5		0.7	0.3	0.1	0.3
Mallinckrodt International Finance S.A.
Condensed Consolidating Financial Statements
Restricted Cash and Investments, Current	0.0		0.0	0.0	0.0
Cash Flows From Operating Activities:
Net cash (used in) provided by operating activities	(94.0)		1,139.4	(47.4)	(148.2)
Cash Flows From Investing Activities:
Capital expenditures	0.0		0.0	0.0	0.0
Acquisitions and intangibles, net of cash acquired	0.0		0.0	0.0	0.0
Proceeds from Divestiture of Businesses, Net of Cash Divested			0.0	234.0
Intercompany Loan Investment	0.0		0.0	(175.2)	0.0
Subsidiary dividend proceeds	0.0		(1,170.0)		0.0
Investment in subsidiary	260.0		(1,475.3)	(861.2)	(3,014.4)
Proceeds from Divestiture of Subsidiary			0.0	0.0
Payments to Acquire Subsidiary			0.0	0.0
Restricted cash			0.0
Other	0.0		0.0	0.0	0.0
Net cash from investing activities	(260.0)		(1,475.3)	(802.4)	(3,014.4)
Cash Flows From Financing Activities:
Issuance of external debt	175.0		1,400.0	0.0	2,890.0
Repayment of capital leases	86.2		(764.5)	(549.2)	(258.3)
Debt financing costs	0.0		(12.7)	0.0	(39.1)
Proceeds from exercise of share options	0.0		0.0	0.0	0.0
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	0.0				0.0
Intercompany loan borrowings	(284.7)		(1,747.4)	(1,271.9)	(703.6)
Capital contribution	0.0		0.0	0.0	0.0
Repurchase of shares	0.0		0.0	0.0	0.0
Other	0.0		0.0	0.0	0.0
Net cash provided by financing activities	373.5		1,200.2	722.7	3,296.2
Effect of currency rate changes on cash	0.0		0.0	0.0	0.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	19.5		864.3	(127.1)	133.6
Cash and cash equivalents	44.5		908.8	25.0	152.1
Restricted Cash and Investments, Noncurrent	0.0		0.0	0.0	0.0
Cash and Cash Equivalents, Including Restricted Cash	44.5		908.8	25.0	152.1	18.5
Other Subsidiaries
Condensed Consolidating Financial Statements
Restricted Cash and Investments, Current	0.1		0.0	0.1	47.7
Cash Flows From Operating Activities:
Net cash (used in) provided by operating activities	272.2		2,274.9	1,214.1	871.7
Cash Flows From Investing Activities:
Capital expenditures	65.2		(186.1)	(182.9)	(148.0)
Acquisitions and intangibles, net of cash acquired	(1.8)		(76.3)	(245.4)	(2,154.7)
Proceeds from Divestiture of Businesses, Net of Cash Divested			576.9	32.7
Intercompany Loan Investment	(424.7)		(1,157.9)	(1,714.5)	(554.2)
Subsidiary dividend proceeds	0.0		(2,750.2)		0.0
Investment in subsidiary	0.0		0.0	0.0	0.0
Proceeds from Divestiture of Subsidiary			0.0	0.0
Payments to Acquire Subsidiary			0.0	(3.4)
Restricted cash			0.0
Other	10.2		3.9	6.0	3.0
Net cash from investing activities	(501.9)		(839.5)	(2,107.5)	(2,853.9)
Cash Flows From Financing Activities:
Issuance of external debt	15.0		65.0	98.3	120.0
Repayment of capital leases	0.5		(152.7)	(19.4)	(1,590.1)
Debt financing costs	0.0		0.0	(0.1)	(0.8)
Proceeds from exercise of share options	0.0		0.0	0.0	0.0
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	0.0				0.0
Intercompany loan borrowings	0.0		0.0	0.0	0.0
Capital contribution	260.0		1,475.3	861.2	3,014.4
Repurchase of shares	0.0		0.0	0.0	0.0
Other	0.0		(21.8)	(53.0)	(28.1)
Net cash provided by financing activities	274.5		(1,384.4)	887.0	1,515.4
Effect of currency rate changes on cash	(3.0)		2.5	0.3	(11.6)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	41.8		53.5	(6.1)	(478.4)
Cash and cash equivalents	297.0		351.4	255.2	213.7
Restricted Cash and Investments, Noncurrent	19.0		18.2	19.0	19.0
Cash and Cash Equivalents, Including Restricted Cash	316.1		369.6	274.3	280.4	758.8
Eliminations
Condensed Consolidating Financial Statements
Restricted Cash and Investments, Current	0.0		0.0	0.0	0.0
Cash Flows From Operating Activities:
Net cash (used in) provided by operating activities	0.0		(3,920.2)	0.0	0.0
Cash Flows From Investing Activities:
Capital expenditures	0.0		0.0	0.0	0.0
Acquisitions and intangibles, net of cash acquired	0.0		0.0	0.0	0.0
Proceeds from Divestiture of Businesses, Net of Cash Divested			0.0	0.0
Intercompany Loan Investment	(424.7)		(1,747.4)	(1,889.7)	(703.6)
Subsidiary dividend proceeds	0.0		(3,920.2)		0.0
Investment in subsidiary	(260.0)		1,475.3	861.2	3,014.4
Proceeds from Divestiture of Subsidiary			0.0	(3.4)
Payments to Acquire Subsidiary			0.0	3.4
Restricted cash			0.0
Other	0.0		0.0	0.0	0.0
Net cash from investing activities	684.7		3,222.7	2,750.9	3,718.0
Cash Flows From Financing Activities:
Issuance of external debt	0.0		0.0	0.0	0.0
Repayment of capital leases	0.0		0.0	0.0	0.0
Debt financing costs	0.0		0.0	0.0	0.0
Proceeds from exercise of share options	0.0		0.0	0.0	0.0
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	0.0				0.0
Intercompany loan borrowings	424.7		1,747.4	1,889.7	703.6
Capital contribution	(260.0)		(1,475.3)	(861.2)	(3,014.4)
Repurchase of shares	0.0		0.0	0.0	0.0
Other	0.0		0.0	0.0	0.0
Net cash provided by financing activities	(684.7)		697.5	(2,750.9)	(3,718.0)
Effect of currency rate changes on cash	0.0		0.0	0.0	0.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	0.0		0.0	0.0	0.0
Cash and cash equivalents	0.0		0.0	0.0	0.0
Restricted Cash and Investments, Noncurrent	0.0		0.0	0.0	0.0
Cash and Cash Equivalents, Including Restricted Cash	$ 0.0		$ 0.0	$ 0.0	$ 0.0	$ 0.0