Summary of Significant Accounting Policies - Estimated Useful Lives (Details) - GSWC	12 Months Ended
	Dec. 31, 2025
Estimated useful lives of utility plant, as authorized by the CPUC
Generation	40 years
Minimum
Estimated useful lives of utility plant, as authorized by the CPUC
Source of water supply	20 years
Pumping	26 years
Water treatment	26 years
Transmission and Distribution	15 years
Other plant	5 years
Maximum
Estimated useful lives of utility plant, as authorized by the CPUC
Source of water supply	60 years
Pumping	41 years
Water treatment	32 years
Transmission and Distribution	80 years
Other plant	62 years