Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Feb. 06, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-13883
Entity Registrant Name	CALIFORNIA WATER SERVICE GROUP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0448994
Entity Address, Address Line One	1720 North First Street
Entity Address, City or Town	San Jose,
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	95112
City Area Code	408
Local Phone Number	367-8200
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	CWT
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 2,122
Entity Common Stock, Shares Outstanding		55,600,905
Documents Incorporated by Reference	Certain information required to be disclosed in Part III of this report is incorporated by reference from the registrant’s definitive Proxy Statement for its Annual Meeting of Stockholders to be held on or about May 31, 2023. The proxy statement is expected to be filed no later than 120 days after the end of the fiscal year covered by this report.
Entity Central Index Key	0001035201
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY