Exit and disposal activities - Restructuring Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2025	May 31, 2024	May 31, 2025	May 31, 2024
Restructuring Cost and Reserve [Line Items]
Costs	$ 73	$ 0	$ 473	$ 0
Footprint Optimization Program
Restructuring Cost and Reserve [Line Items]
Costs	73		473
Footprint Optimization Program | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	74		466
Footprint Optimization Program | Operating Segments | International
Restructuring Cost and Reserve [Line Items]
Costs	(1)		0
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	53		259
Footprint Optimization Program | Lease obligations and other real estate costs | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	52		255
Footprint Optimization Program | Lease obligations and other real estate costs | Operating Segments | International
Restructuring Cost and Reserve [Line Items]
Costs	1		4
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	(2)		135
Footprint Optimization Program | Asset impairments | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	0		139
Footprint Optimization Program | Asset impairments | Operating Segments | International
Restructuring Cost and Reserve [Line Items]
Costs	(2)		(5)
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	22		79
Footprint Optimization Program | Employee severance and other exit costs | Operating Segments | U.S. Retail Pharmacy
Restructuring Cost and Reserve [Line Items]
Costs	22		72
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