Exit and disposal activities - Restructuring Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Feb. 28, 2025	Feb. 29, 2024	Feb. 28, 2025	Feb. 29, 2024
Restructuring Cost and Reserve [Line Items]
Costs	$ 68	$ 0	$ 400	$ 0
Footprint Optimization Program
Restructuring Cost and Reserve [Line Items]
Costs	68		400
Footprint Optimization Program | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	70		392
Footprint Optimization Program | Operating Segments | International
Restructuring Cost and Reserve [Line Items]
Costs	(2)		1
Footprint Optimization Program | Operating Segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Costs	0		4
Footprint Optimization Program | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Costs	0		3
Footprint Optimization Program | Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Costs	42		206
Footprint Optimization Program | Lease obligations and other real estate costs | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	41		203
Footprint Optimization Program | Lease obligations and other real estate costs | Operating Segments | International
Restructuring Cost and Reserve [Line Items]
Costs	1		3
Footprint Optimization Program | Lease obligations and other real estate costs | Operating Segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Costs	0		0
Footprint Optimization Program | Lease obligations and other real estate costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Costs	0		0
Footprint Optimization Program | Asset impairments
Restructuring Cost and Reserve [Line Items]
Costs	10		137
Footprint Optimization Program | Asset impairments | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	13		139
Footprint Optimization Program | Asset impairments | Operating Segments | International
Restructuring Cost and Reserve [Line Items]
Costs	(3)		(3)
Footprint Optimization Program | Asset impairments | Operating Segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Costs	0		1
Footprint Optimization Program | Asset impairments | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Costs	0		0
Footprint Optimization Program | Employee severance and other exit costs
Restructuring Cost and Reserve [Line Items]
Costs	16		57
Footprint Optimization Program | Employee severance and other exit costs | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	16		50
Footprint Optimization Program | Employee severance and other exit costs | Operating Segments | International
Restructuring Cost and Reserve [Line Items]
Costs	0		1
Footprint Optimization Program | Employee severance and other exit costs | Operating Segments | U.S. Healthcare
Restructuring Cost and Reserve [Line Items]
Costs	0		3
Footprint Optimization Program | Employee severance and other exit costs | Corporate and Other
Restructuring Cost and Reserve [Line Items]
Costs	$ 0		$ 3