CONDENSED CONSOLIDATING FINANCIAL STATEMENTS (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012 Cal Water	Dec. 31, 2011 Cal Water	Dec. 31, 2010 Cal Water	Dec. 31, 2012 All Other Subsidiaries	Dec. 31, 2011 All Other Subsidiaries	Dec. 31, 2010 All Other Subsidiaries	Dec. 31, 2012 First Mortgage Bonds, 5.875% due 2019	Dec. 31, 2011 First Mortgage Bonds, 5.875% due 2019	Apr. 17, 2009 First Mortgage Bonds, 5.875% due 2019 Cal Water	Dec. 31, 2012 First Mortgage Bonds, 5.500% due 2040	Dec. 31, 2011 First Mortgage Bonds, 5.500% due 2040	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%	5.875%	5.875%	5.50%	5.50%	5.50%
Ownership interest (as a percent)	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%