Condensed Consolidating Financial Statements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013 Cal Water	Dec. 31, 2012 Cal Water	Sep. 30, 2013 All Other Subsidiaries	Dec. 31, 2012 All Other Subsidiaries	Sep. 30, 2013 First Mortgage Bonds, 5.875% due 2019 Cal Water	Apr. 17, 2009 First Mortgage Bonds, 5.875% due 2019 Cal Water	Sep. 30, 2013 First Mortgage Bonds, 5.500% due 2040 Cal Water	Nov. 17, 2010 First Mortgage Bonds, 5.500% due 2040 Cal Water
Long-term debt
Debt issued						$ 100		$ 100
Interest rate (as a percent)					5.875%		5.50%
Ownership interest (as a percent)	100.00%	100.00%	100.00%	100.00%