Revenue and segment information - Disaggregation of Net Sales (Details) - United States - Customer Concentration Risk - Revenue, Segment Benchmark	3 Months Ended
	Oct. 31, 2025	Oct. 31, 2024
Segment Reporting Information [Line Items]
Concentration risk, percentage	100.00%	100.00%
Waterworks
Segment Reporting Information [Line Items]
Concentration risk, percentage	25.00%	23.00%
Ferguson Home
Segment Reporting Information [Line Items]
Concentration risk, percentage	21.00%	21.00%
Commercial/Mechanical
Segment Reporting Information [Line Items]
Concentration risk, percentage	15.00%	13.00%
Residential Trade Plumbing
Segment Reporting Information [Line Items]
Concentration risk, percentage	14.00%	16.00%
HVAC
Segment Reporting Information [Line Items]
Concentration risk, percentage	11.00%	13.00%
Industrial
Segment Reporting Information [Line Items]
Concentration risk, percentage	7.00%	7.00%
Facilities Supply
Segment Reporting Information [Line Items]
Concentration risk, percentage	4.00%	4.00%
Fire & Fabrication
Segment Reporting Information [Line Items]
Concentration risk, percentage	3.00%	3.00%