Fair value measurements - assets and liabilities on a recurring basis (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 26, 2015	Jun. 27, 2015	Nov. 08, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value, Assets, Level 1, Level 2, Level 3 Transfers, Amount	$ 0	$ 0
Senior Notes	4,722,700,000	4,720,900,000	$ 2,300,000,000
Long-term Debt	822,700,000	820,900,000
Debt Instrument, Fair Value Disclosure	890,900,000	902,400,000
Assets:
Investment securities	16,500,000	12,700,000
Foreign currency forward contracts	4,800,000	12,400,000
Funds associated with Israeli post employment benefits	16,500,000	17,300,000
Total assets	37,800,000	42,400,000
Liabilities:
Foreign currency forward contracts	5,900,000	4,600,000
Total liabilities	5,900,000	4,600,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Senior Notes	3,900,000,000	3,900,000,000
Debt Instrument, Fair Value Disclosure	3,811,500,000	3,850,700,000
Assets:
Investment securities	16,500,000	12,700,000
Foreign currency forward contracts	0	0
Funds associated with Israeli post employment benefits	0	0
Total assets	16,500,000	12,700,000
Liabilities:
Foreign currency forward contracts	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Investment securities	0	0
Foreign currency forward contracts	4,800,000	12,400,000
Funds associated with Israeli post employment benefits	16,500,000	17,300,000
Total assets	21,300,000	29,700,000
Liabilities:
Foreign currency forward contracts	5,900,000	4,600,000
Total liabilities	5,900,000	4,600,000
Fair Value, Inputs, Level 3 [Member]
Assets:
Investment securities	0	0
Foreign currency forward contracts	0	0
Funds associated with Israeli post employment benefits	0	0
Total assets	0	0
Liabilities:
Foreign currency forward contracts	0	0
Total liabilities	$ 0	$ 0