Accounting policies - Property, plant and equipment (Details)	Dec. 31, 2023
Property, Plant and Equipment, Estimated Useful Lives	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember
Building [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	40 years
Building [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	5 years
Plant And Equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	40 years
Plant And Equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	4 years
Distribution Systems [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	40 years
Distribution Systems [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Office furniture, fixtures and equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	10 years
Office furniture, fixtures and equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Vehicles [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	10 years
Vehicles [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	3 years
Lab equipment [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life	10 years
Lab equipment [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life	5 years