Condensed Consolidating and Combining Financial Statements (Schedule of Condensed Consolidating and Combining Statements of Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 30, 2016	Sep. 30, 2016	Jun. 24, 2016	Mar. 25, 2016	Dec. 25, 2015	Dec. 29, 2017	Sep. 30, 2016	Sep. 25, 2015
Condensed Consolidating Financial Statements
Net sales	$ 792.3	$ 793.9	$ 824.5	$ 810.9	$ 829.9	$ 887.2	$ 866.6	$ 815.8	$ 811.2	$ 3,221.6	$ 3,380.8	$ 2,923.1
Cost of sales					384.1				360.3	1,565.3	1,525.8	1,300.2
Gross profit	421.0	400.6	416.1	418.6	445.8	490.2	488.8	425.1	450.9	1,656.3	1,855.0	1,622.9
Selling, general and administrative expenses					368.3				223.3	920.9	925.3	1,023.8
Research and development expenses					66.2				61.4	277.3	262.2	203.3
Separation costs					0.0					0.0	0.0	0.0
Restructuring charges, net					3.8				4.1	31.2	33.3	45.0
Non-restructuring impairment charges					214.3					63.7	16.9	0.0
Gain on divestiture and license					0.0					(56.9)	0.0	(3.0)
Operating income (loss)					(206.8)				(162.1)	420.1	617.3	353.8
Interest expense					(91.3)				(97.8)	(369.1)	(384.6)	(255.6)
Interest income					0.5				0.2	4.6	1.3	1.0
Other income (expense), net					(0.9)				2.0	6.0	(0.6)	8.1
Intercompany interest and fees					0.0					0.0	0.0	0.0
Equity in net income of subsidiaries					0.0					0.0	0.0	0.0
Income (loss) from continuing operations before income taxes					(298.5)				66.5	61.6	233.4	107.3
Income Tax Expense (Benefit)					(121.7)				(37.3)	(1,709.6)	(255.6)	(129.3)
Income (loss) from continuing operations	1,607.4	64.3	70.6	28.9	(176.8)	110.0	176.7	98.5	103.8	1,771.2	489.0	236.6
Income (loss) from discontinued operations, net of income taxes	1.3	(0.6)	(7.8)	370.3	23.6	5.0	22.6	19.8	107.3	363.2	154.7	88.1
Net income (loss)	$ 1,608.7	$ 63.7	$ 62.8	$ 399.2	(153.2)	$ 115.0	$ 199.3	$ 118.3	$ 211.1	2,134.4	643.7	324.7
Other comprehensive loss, net of tax					13.1					59.6	(86.5)	(64.8)
Comprehensive income (loss)					(140.1)					2,194.0	557.2	259.9
Mallinckrodt plc
Condensed Consolidating Financial Statements
Net sales					0.0					0.0	0.0	0.0
Cost of sales					0.0					2.6	0.0	0.0
Gross profit					0.0					(2.6)	0.0	0.0
Selling, general and administrative expenses					13.4					59.5	51.3	116.3
Research and development expenses					0.0					5.1	0.0	0.0
Separation costs					0.0					0.0	0.0	0.0
Restructuring charges, net					0.0					0.0	0.0	9.8
Non-restructuring impairment charges					0.0					0.0	0.0	0.0
Gain on divestiture and license					0.0					0.0	0.0	0.0
Operating income (loss)					(13.4)					(67.2)	(51.3)	(126.1)
Interest expense					(2.9)					(13.8)	(230.3)	96.4
Interest income					0.0					7.3	0.0	0.0
Other income (expense), net					1.8					20.3	90.0	216.3
Intercompany interest and fees					4.4					18.3	16.1	14.7
Equity in net income of subsidiaries					(136.5)					2,200.0	820.8	330.6
Income (loss) from continuing operations before income taxes					(155.4)					2,128.3	613.1	309.7
Income Tax Expense (Benefit)					(2.2)					(6.1)	(30.6)	(15.9)
Income (loss) from continuing operations					(153.2)					2,134.4	643.7	325.6
Income (loss) from discontinued operations, net of income taxes					0.0					0.0	0.0	(0.9)
Net income (loss)					(153.2)					2,134.4	643.7	324.7
Other comprehensive loss, net of tax					13.1					59.6	(86.5)	(64.8)
Comprehensive income (loss)					(140.1)					2,194.0	557.2	259.9
Mallinckrodt International Finance S.A.
Condensed Consolidating Financial Statements
Net sales					0.0					0.0	0.0	0.0
Cost of sales					0.0					0.0	0.0	0.0
Gross profit					0.0					0.0	0.0	0.0
Selling, general and administrative expenses					0.2					0.7	0.8	15.7
Research and development expenses					0.0					0.0	0.0	0.0
Separation costs					0.0					0.0	0.0	0.0
Restructuring charges, net					0.0					0.0	0.0	0.0
Non-restructuring impairment charges					0.0					0.0	0.0	0.0
Gain on divestiture and license					0.0					0.0	0.0	0.0
Operating income (loss)					(0.2)					(0.7)	(0.8)	(15.7)
Interest expense					(81.1)					(353.9)	(327.0)	(230.2)
Interest income					0.1					1.2	0.5	0.1
Other income (expense), net					0.7					(1.7)	1.7	0.0
Intercompany interest and fees					0.0					0.0	0.0	0.0
Equity in net income of subsidiaries					35.2					2,901.8	1,327.2	496.3
Income (loss) from continuing operations before income taxes					(45.3)					2,546.7	1,001.6	250.5
Income Tax Expense (Benefit)					(0.3)					(5.3)	(18.1)	0.0
Income (loss) from continuing operations					(45.0)					2,552.0	1,019.7	250.5
Income (loss) from discontinued operations, net of income taxes					0.4					(2.1)	38.2	0.0
Net income (loss)					(44.6)					2,549.9	1,057.9	250.5
Other comprehensive loss, net of tax					13.1					59.6	(86.5)	(64.8)
Comprehensive income (loss)					(31.5)					2,609.5	971.4	185.7
Other Subsidiaries
Condensed Consolidating Financial Statements
Net sales					829.9					3,221.6	3,380.8	2,923.1
Cost of sales					384.1					1,562.7	1,525.8	1,300.2
Gross profit					445.8					1,658.9	1,855.0	1,622.9
Selling, general and administrative expenses					354.7					860.7	873.2	891.8
Research and development expenses					66.2					272.2	262.2	203.3
Separation costs					0.0					0.0	0.0	0.0
Restructuring charges, net					3.8					31.2	33.3	35.2
Non-restructuring impairment charges					214.3					63.7	16.9	0.0
Gain on divestiture and license					0.0					(56.9)	0.0	(3.0)
Operating income (loss)					(193.2)					488.0	669.4	495.6
Interest expense					(17.9)					(74.2)	(82.4)	(25.2)
Interest income					11.0					68.9	255.9	97.1
Other income (expense), net					(3.4)					(12.6)	(92.3)	(208.2)
Intercompany interest and fees					(4.4)					(18.3)	(16.1)	(14.7)
Equity in net income of subsidiaries					(44.5)					2,549.9	1,057.9	250.5
Income (loss) from continuing operations before income taxes					(243.6)					3,038.3	1,824.6	624.5
Income Tax Expense (Benefit)					(119.2)					(1,698.2)	(206.9)	(113.4)
Income (loss) from continuing operations					(124.4)					4,736.5	2,031.5	737.9
Income (loss) from discontinued operations, net of income taxes					23.2					365.3	116.5	89.0
Net income (loss)					(101.2)					5,101.8	2,148.0	826.9
Other comprehensive loss, net of tax					26.0					118.2	(173.5)	(69.9)
Comprehensive income (loss)					(75.2)					5,220.0	1,974.5	757.0
Eliminations
Condensed Consolidating Financial Statements
Net sales					0.0					0.0	0.0	0.0
Cost of sales					0.0					0.0	0.0	0.0
Gross profit					0.0					0.0	0.0	0.0
Selling, general and administrative expenses					0.0					0.0	0.0	0.0
Research and development expenses					0.0					0.0	0.0	0.0
Separation costs					0.0					0.0	0.0	0.0
Restructuring charges, net					0.0					0.0	0.0	0.0
Non-restructuring impairment charges					0.0					0.0	0.0	0.0
Gain on divestiture and license					0.0					0.0	0.0	0.0
Operating income (loss)					0.0					0.0	0.0	0.0
Interest expense					10.6					72.8	255.1	96.2
Interest income					(10.6)					(72.8)	(255.1)	(96.2)
Other income (expense), net					0.0					0.0	0.0	0.0
Intercompany interest and fees					0.0					0.0	0.0	0.0
Equity in net income of subsidiaries					145.8					(7,651.7)	(3,205.9)	(1,077.4)
Income (loss) from continuing operations before income taxes					145.8					(7,651.7)	(3,205.9)	(1,077.4)
Income Tax Expense (Benefit)					0.0					0.0	0.0	0.0
Income (loss) from continuing operations					145.8					(7,651.7)	(3,205.9)	(1,077.4)
Income (loss) from discontinued operations, net of income taxes					0.0					0.0	0.0	0.0
Net income (loss)					145.8					(7,651.7)	(3,205.9)	(1,077.4)
Other comprehensive loss, net of tax					(39.1)					(177.8)	260.0	134.7
Comprehensive income (loss)					$ 106.7					$ (7,829.5)	$ (2,945.9)	$ (942.7)