Exit and disposal activities - Narrative (Details) $ in Millions			3 Months Ended		30 Months Ended
	Dec. 20, 2018 USD ($)	Oct. 24, 2017 store	Nov. 30, 2020 USD ($) store	Nov. 30, 2019 USD ($)	Aug. 31, 2020 USD ($) store	Sep. 01, 2019 USD ($)	Aug. 31, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			$ (20,563)	$ (24,314)	$ (21,136)		$ (24,152)
Cumulative Effect, Period of Adoption, Adjustment
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings					5		442
Retained earnings
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings			(33,495)	(35,810)	(34,210)		(35,815)
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings					$ 3		$ 442
Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			1,200
Restructuring costs			$ 83	64
Transformational Cost Management Program | UNITED KINGDOM
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store			200
Transformational Cost Management Program | UNITED STATES
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store			250
Transformational Cost Management Program | Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Restructuring Cost and Reserve [Line Items]
Cumulative effect adjustment to decrease retained earnings						$ 508
Store Optimization Program
Restructuring Cost and Reserve [Line Items]
Number of stores expected to close | store		600
Number of stores closed | store					769
Lease obligations and other real estate costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			$ 264
Restructuring costs			22	1
Lease obligations and other real estate costs | Store Optimization Program
Restructuring Cost and Reserve [Line Items]
Restructuring costs				3
Asset impairments | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			354
Restructuring costs			4	11
Employee severance and business transition costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			471
Restructuring costs			51	40
Information technology transformation and other exit costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Costs incurred			146
Restructuring costs			6	12
Employee severance and other exit costs | Store Optimization Program
Restructuring Cost and Reserve [Line Items]
Restructuring costs				$ 6
Minimum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected annual cost savings of restructuring plan	$ 2,000
Expected cost			2,100
Minimum | Exit and disposal costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			1,800
Maximum | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			2,400
Maximum | Exit and disposal costs | Transformational Cost Management Program
Restructuring Cost and Reserve [Line Items]
Expected cost			$ 2,100