Condensed Consolidating and Combining Financial Statements (Schedule of Condensed Consolidating Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 29, 2017	Dec. 30, 2016	Sep. 30, 2016	Dec. 25, 2015	Sep. 25, 2015	Sep. 26, 2014
Current Assets:
Cash and cash equivalents	$ 1,260.9	$ 342.0	$ 280.5	$ 521.9	$ 365.9
Accounts receivable, net	445.8	431.0
Inventories	340.4	350.7
Deferred income taxes	0.0	0.0
Prepaid expenses and other current assets	84.1	131.9
Notes, Loans and Financing Receivable, Net, Current	154.0	0.0
Current assets held for sale	0.0	310.9
Intercompany receivable	0.0	0.0
Total current assets	2,285.2	1,566.5
Property, plant and equipment, net	966.8	881.5
Goodwill	3,482.7	3,498.1
Intangible assets, net	8,375.0	9,000.5
Long-term assets held for sale	0.0	0.0
Investment in subsidiaries	0.0	0.0
Intercompany loan receivable	0.0	0.0
Other assets	171.2	259.7
Total Assets	15,280.9	15,206.3
Current Liabilities:
Current maturities of long-term debt	313.7	271.2
Accounts payable	113.3	112.1
Accrued payroll and payroll-related costs	98.5	76.1
Interest Payable, Current	57.0	68.7
Taxes Payable, Current	15.8	101.7
Accrued and other current liabilities	452.1	557.1
Current liabilities held for sale	0.0	120.3
Intercompany payable	0.0	0.0
Total current liabilities	1,050.4	1,307.2
Long-term debt	6,420.9	5,880.8
Pension and postretirement benefits	67.1	136.4
Environmental liabilities	73.2	73.0
Deferred income taxes	689.0	2,398.1
Other income tax liabilities	94.1	70.4
Long-term liabilities held for sale	0.0	0.0
Intercompany loans payable	0.0	0.0
Other liabilities	364.2	356.1
Total Liabilities	8,758.9	10,222.0
Shareholders' equity	6,522.0	4,984.3	5,270.7		5,311.2	$ 4,958.0
Total Liabilities and Shareholders' Equity	15,280.9	15,206.3
Mallinckrodt plc
Current Assets:
Cash and cash equivalents	0.7	0.5	0.3		0.1
Accounts receivable, net	0.0	0.0
Inventories	0.0	0.0
Deferred income taxes	0.0	0.0
Prepaid expenses and other current assets	1.0	1.0
Notes, Loans and Financing Receivable, Net, Current	0.0	0.0
Current assets held for sale	0.0	0.0
Intercompany receivable	70.0	59.7
Total current assets	71.7	61.2
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intangible assets, net	0.0	0.0
Long-term assets held for sale	0.0	0.0
Investment in subsidiaries	6,551.6	5,534.1
Intercompany loan receivable	593.1	3.5
Other assets	0.0	0.0
Total Assets	7,216.4	5,598.8
Current Liabilities:
Current maturities of long-term debt	0.0	0.0
Accounts payable	0.1	0.1
Accrued payroll and payroll-related costs	0.0	0.0
Interest Payable, Current	0.0	0.0
Taxes Payable, Current	0.0	0.0
Accrued and other current liabilities	0.8	1.9
Current liabilities held for sale	0.0	0.0
Intercompany payable	693.5	612.5
Total current liabilities	694.4	614.5
Long-term debt	0.0	0.0
Pension and postretirement benefits	0.0	0.0
Environmental liabilities	0.0	0.0
Deferred income taxes	0.0	0.0
Other income tax liabilities	0.0	0.0
Long-term liabilities held for sale	0.0	0.0
Intercompany loans payable	0.0	0.0
Other liabilities	0.0	0.0
Total Liabilities	694.4	614.5
Shareholders' equity	6,522.0	4,984.3
Total Liabilities and Shareholders' Equity	7,216.4	5,598.8
Mallinckrodt International Finance S.A.
Current Assets:
Cash and cash equivalents	908.8	44.5	25.0		152.1
Accounts receivable, net	0.0	0.0
Inventories	0.0	0.0
Deferred income taxes	0.0	0.0
Prepaid expenses and other current assets	0.2	0.0
Notes, Loans and Financing Receivable, Net, Current	0.0	0.0
Current assets held for sale	0.0	0.0
Intercompany receivable	173.4	65.1
Total current assets	1,082.4	109.6
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intangible assets, net	0.0	0.0
Long-term assets held for sale	0.0	0.0
Investment in subsidiaries	23,217.8	20,624.1
Intercompany loan receivable	0.0	0.0
Other assets	0.0	0.0
Total Assets	24,300.2	20,733.7
Current Liabilities:
Current maturities of long-term debt	313.5	19.7
Accounts payable	0.0	0.1
Accrued payroll and payroll-related costs	0.0	0.0
Interest Payable, Current	53.0	53.9
Taxes Payable, Current	0.0	0.0
Accrued and other current liabilities	0.4	7.5
Current liabilities held for sale	0.0	0.0
Intercompany payable	104.6	467.1
Total current liabilities	471.5	548.3
Long-term debt	6,206.8	5,860.6
Pension and postretirement benefits	0.0	0.0
Environmental liabilities	0.0	0.0
Deferred income taxes	0.0	0.0
Other income tax liabilities	0.0	0.0
Long-term liabilities held for sale	0.0	0.0
Intercompany loans payable	5,257.9	3,329.4
Other liabilities	7.8	7.0
Total Liabilities	11,944.0	9,745.3
Shareholders' equity	12,356.2	10,988.4
Total Liabilities and Shareholders' Equity	24,300.2	20,733.7
Other Subsidiaries
Current Assets:
Cash and cash equivalents	351.4	297.0	255.2		213.7
Accounts receivable, net	445.8	431.0
Inventories	340.4	350.7
Deferred income taxes	0.0	0.0
Prepaid expenses and other current assets	82.9	130.9
Notes, Loans and Financing Receivable, Net, Current	154.0	0.0
Current assets held for sale		310.9
Intercompany receivable	831.4	1,081.3
Total current assets	2,205.9	2,601.8
Property, plant and equipment, net	966.8	881.5
Goodwill	3,482.7	3,498.1
Intangible assets, net	8,375.0	9,000.5
Long-term assets held for sale	0.0	0.0
Investment in subsidiaries	12,356.2	10,988.5
Intercompany loan receivable	4,664.8	3,325.9
Other assets	171.2	259.7
Total Assets	32,222.6	30,556.0
Current Liabilities:
Current maturities of long-term debt	0.2	251.5
Accounts payable	113.2	111.9
Accrued payroll and payroll-related costs	98.5	76.1
Interest Payable, Current	4.0	14.8
Taxes Payable, Current	15.8	101.7
Accrued and other current liabilities	450.9	547.7
Current liabilities held for sale	0.0	120.3
Intercompany payable	276.7	126.5
Total current liabilities	959.3	1,350.5
Long-term debt	214.1	20.2
Pension and postretirement benefits	67.1	136.4
Environmental liabilities	73.2	73.0
Deferred income taxes	689.0	2,398.1
Other income tax liabilities	94.1	70.4
Long-term liabilities held for sale	0.0	0.0
Intercompany loans payable	0.0	0.0
Other liabilities	356.4	349.1
Total Liabilities	2,453.2	4,397.7
Shareholders' equity	29,769.4	26,158.3
Total Liabilities and Shareholders' Equity	32,222.6	30,556.0
Eliminations
Current Assets:
Cash and cash equivalents	0.0	0.0	$ 0.0		$ 0.0
Accounts receivable, net	0.0	0.0
Inventories	0.0	0.0
Deferred income taxes	0.0	0.0
Prepaid expenses and other current assets	0.0	0.0
Notes, Loans and Financing Receivable, Net, Current	0.0	0.0
Current assets held for sale	0.0	0.0
Intercompany receivable	(1,074.8)	(1,206.1)
Total current assets	(1,074.8)	(1,206.1)
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intangible assets, net	0.0	0.0
Long-term assets held for sale	0.0	0.0
Investment in subsidiaries	(42,125.6)	(37,146.7)
Intercompany loan receivable	(5,257.9)	(3,329.4)
Other assets	0.0	0.0
Total Assets	(48,458.3)	(41,682.2)
Current Liabilities:
Current maturities of long-term debt	0.0	0.0
Accounts payable	0.0	0.0
Accrued payroll and payroll-related costs	0.0	0.0
Interest Payable, Current	0.0	0.0
Taxes Payable, Current	0.0	0.0
Accrued and other current liabilities	0.0	0.0
Current liabilities held for sale	0.0	0.0
Intercompany payable	(1,074.8)	(1,206.1)
Total current liabilities	(1,074.8)	(1,206.1)
Long-term debt	0.0	0.0
Pension and postretirement benefits	0.0	0.0
Environmental liabilities	0.0	0.0
Deferred income taxes	0.0	0.0
Other income tax liabilities	0.0	0.0
Long-term liabilities held for sale	0.0	0.0
Intercompany loans payable	(5,257.9)	(3,329.4)
Other liabilities	0.0	0.0
Total Liabilities	(6,332.7)	(4,535.5)
Shareholders' equity	(42,125.6)	(37,146.7)
Total Liabilities and Shareholders' Equity	$ (48,458.3)	$ (41,682.2)