Consolidated and Combined Statement of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Ordinary Shares	Treasury Shares	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income
Beginning balance, shares at Sep. 26, 2014		116,200,000	200,000
Beginning balance, value at Sep. 26, 2014	$ 4,958.0	$ 23.2	$ (17.5)	$ 5,172.4	$ (285.8)	$ 65.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	324.7				324.7
Currency translation adjustments	(70.8)					(70.8)
Change in derivatives, net of tax	0.4					0.4
Minimum pension liability, net of tax	5.6					5.6
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	0.0
Treasury Stock, Shares, Retired		(1,200,000)
Stock Repurchased and Retired During Period, Value	$ 0.0	$ (0.2)		(0.2)
Share options exercised, shares	1,132,778	1,200,000
Share options exercised, value	$ 34.4	$ 0.2		34.2
Vesting of restricted shares, shares		1,300,000
Vesting of restricted shares, value	0.0	$ (0.3)		(0.3)
Adjustments to Additional Paid in Capital, Income Tax Deficiency from Share-based Compensation	34.1			34.1
Treasury Stock, Shares, Acquired			1,000,000
Treasury Stock, Value, Acquired, Cost Method	(92.2)		$ (92.2)
Share-based compensation	117.0			117.0
Ending balance, shares at Sep. 25, 2015		117,500,000	1,200,000
Ending balance, value at Sep. 25, 2015	5,311.2	$ 23.5	$ (109.7)	5,357.6	38.9	0.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	643.7				643.7
Currency translation adjustments	(58.6)					(58.6)
Change in derivatives, net of tax	0.5					0.5
Minimum pension liability, net of tax	(28.4)					(28.4)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	$ 0.0
Share options exercised, shares	413,830	400,000
Share options exercised, value	$ 14.0	$ 0.1		13.9
Vesting of restricted shares, shares		200,000
Vesting of restricted shares, value	0.0	$ 0.0		0.0
Adjustments to Additional Paid in Capital, Income Tax Deficiency from Share-based Compensation	$ (1.7)			(1.7)
Treasury Stock, Shares, Acquired	9,800,000
Treasury Stock, Value, Acquired, Cost Method	$ (652.9)
Share-based compensation	42.9			42.9
Ending balance, shares at Sep. 30, 2016		118,100,000	11,000,000
Ending balance, value at Sep. 30, 2016	5,270.7	$ 23.6	$ (762.6)	5,412.7	682.6	(85.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(153.2)				(153.2)
Currency translation adjustments	(21.1)					(21.1)
Change in derivatives, net of tax	0.2					0.2
Minimum pension liability, net of tax	34.0					34.0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	$ 0.0
Share options exercised, shares	16,382	100,000
Share options exercised, value	$ 0.4	$ 0.0		0.4
Vesting of restricted shares, value	0.0
Adjustments to Additional Paid in Capital, Income Tax Deficiency from Share-based Compensation	$ (0.1)			(0.1)
Treasury Stock, Shares, Acquired	2,500,000
Treasury Stock, Value, Acquired, Cost Method	$ (158.8)		158.8
Share-based compensation	11.0			11.0
Stock Issued During Period, Value, Treasury Stock Reissued	(1.2)		$ (1.6)		(0.4)
Ending balance, shares at Dec. 30, 2016		118,200,000	13,500,000
Ending balance, value at Dec. 30, 2016	4,984.3	$ 23.6	$ (919.8)	5,424.0	529.0	(72.5)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(72.1)				(72.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,134.4
Currency translation adjustments	11.3					11.3
Change in derivatives, net of tax	1.0					1.0
Minimum pension liability, net of tax	45.8					45.8
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	1.5					1.5
Treasury Stock, Shares, Retired		(26,500,000)
Stock Repurchased and Retired During Period, Value	$ 0.0	$ (5.3)		(5.3)
Treasury Stock, Shares, Retired			(26,500,000)
Share options exercised, shares	113,605	100,000
Share options exercised, value	$ 4.1	$ 0.0		4.1
Vesting of restricted shares, shares		400,000
Vesting of restricted shares, value	(0.1)	$ (0.1)		0.0
Treasury Stock, Shares, Acquired			18,900,000
Treasury Stock, Value, Acquired, Cost Method	(651.7)		$ (651.7)
Share-based compensation	59.2			59.2
Stock Issued During Period, Value, Treasury Stock Reissued	(4.1)		$ (6.8)		(2.7)
Ending balance, shares at Dec. 29, 2017		92,200,000	5,900,000
Ending balance, value at Dec. 29, 2017	$ 6,522.0	$ 18.4	$ (1,564.7)	$ 5,492.6	$ 2,588.6	$ (12.9)