Commitments and contingencies (Details) $ in Millions		12 Months Ended
	Sep. 28, 2018 USD ($)	Aug. 31, 2018 lawsuit	Aug. 31, 2017 lawsuit
Rite Aid Transactions
Loss Contingencies [Line Items]
Number of lawsuits filed			2
Pennsylvania Court of Common Pleas of Cumberland County
Loss Contingencies [Line Items]
Number of lawsuits filed			1
Middle District of Pennsylvania
Loss Contingencies [Line Items]
Number of lawsuits filed			1
Delaware Court of Chancery
Loss Contingencies [Line Items]
Lawsuits filed and dismissed		8
Subsequent Event
Loss Contingencies [Line Items]
Payments for legal settlements | $	$ 34.5