Line of Credit Facility, Incremental Expansion of Borrowing Capacity

No definition available.

Name:	cwt_LineofCreditFacilityIncrementalExpansionofBorrowingCapacity
Namespace Prefix:	cwt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate during the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cwt_SeriesZZZMortgageBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cwt_Series1MortgageBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=cwt_CalWaterMember
Namespace Prefix:
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Short-term and Long-term Borrowings (Details) - USD ($)			6 Months Ended
Short-term and Long-term Borrowings (Details) - USD ($)	May 11, 2021	Mar. 29, 2019	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Secured Debt
Debt Instrument [Line Items]
Debt issued	$ 280,000,000.0
Secured Debt \| Series ZZZ Mortgage Bonds
Debt Instrument [Line Items]
Debt issued	$ 130,000,000.0
Interest rate	2.87%
Secured Debt \| Series 1 Mortgage Bonds
Debt Instrument [Line Items]
Debt issued	$ 150,000,000.0
Interest rate	3.02%
Parent Company
Debt Instrument [Line Items]
Outstanding borrowings			$ 95,000,000.0		$ 100,000,000.0
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 550,000,000.0
Debt instrument, term		5 years
Average borrowing rate			0.99%	2.13%
Revolving Credit Facility \| Parent Company
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 150,000,000.0
Incremental expansion of borrowing capacity		50,000,000.0
Cal Water
Debt Instrument [Line Items]
Outstanding borrowings			$ 50,000,000.0		$ 270,000,000.0
Cal Water \| Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		400,000,000.0
Incremental expansion of borrowing capacity		$ 150,000,000.0