Exit and disposal activities - narrative (Details) - Store Optimization Program $ in Millions	Oct. 24, 2017 USD ($)	Nov. 30, 2018 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of locations closed	600
Duration of restructuring plan	18 months
Expected cost	$ 450	$ 350
Costs incurred		120
Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Expected cost		160
Costs incurred		12
Employee severance and other exit costs
Restructuring Cost and Reserve [Line Items]
Expected cost		190
Costs incurred		$ 108