Accounting policies - Property, plant and equipment, net (Details) - USD ($)	12 Months Ended	24 Months Ended
	Dec. 31, 2023	Dec. 31, 2024
Property, Plant and Equipment, Estimated Useful Lives		us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember
Interest capitalized	$ 0	$ 0
Buildings | Maximum
Property, Plant and Equipment, Useful Life		40 years
Buildings | Minimum
Property, Plant and Equipment, Useful Life		5 years
Plant and equipment | Maximum
Property, Plant and Equipment, Useful Life		40 years
Plant and equipment | Minimum
Property, Plant and Equipment, Useful Life		4 years
Distribution system | Maximum
Property, Plant and Equipment, Useful Life		40 years
Distribution system | Minimum
Property, Plant and Equipment, Useful Life		3 years
Office furniture, fixtures and equipment | Maximum
Property, Plant and Equipment, Useful Life		10 years
Office furniture, fixtures and equipment | Minimum
Property, Plant and Equipment, Useful Life		3 years
Vehicles | Maximum
Property, Plant and Equipment, Useful Life		10 years
Vehicles | Minimum
Property, Plant and Equipment, Useful Life		3 years
Lab equipment | Maximum
Property, Plant and Equipment, Useful Life		10 years
Lab equipment | Minimum
Property, Plant and Equipment, Useful Life		5 years