Area in which subsidiary generates transmits and distributes electricity to retail electric customers.

No definition available.

Name:	tep_AreaInWhichSubsidiaryGeneratesTransmitsAndDistributesElectricityToRetailElectricCustomers
Namespace Prefix:	tep_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	duration

- Definition

Entity number of customers.

+ References

No definition available.

+ Details

Name:	tep_EntityNumberOfCustomers
Namespace Prefix:	tep_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Income Tax Expense (Benefit), Production Tax Credit

+ References

No definition available.

+ Details

Name:	tep_IncomeTaxExpenseBenefitProductionTaxCredit
Namespace Prefix:	tep_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Investment Tax Credit, Additional Bonus Credit, Percent

+ References

No definition available.

+ Details

Name:	tep_InvestmentTaxCreditAdditionalBonusCreditPercent
Namespace Prefix:	tep_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Investment Tax Credit Sold

+ References

No definition available.

+ Details

Name:	tep_InvestmentTaxCreditSold
Namespace Prefix:	tep_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Operations And Maintenance Expense, Excluding Customer Funded Expenses

+ References

No definition available.

+ Details

Name:	tep_OperationsAndMaintenanceExpenseExcludingCustomerFundedExpenses
Namespace Prefix:	tep_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Proceeds From Sale Of Investment Tax Credit

+ References

No definition available.

+ Details

Name:	tep_ProceedsFromSaleOfInvestmentTaxCredit
Namespace Prefix:	tep_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-2

+ Details

Name:	us-gaap_DeferredTaxAssetsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-2

+ Details

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

- Definition

The amount deducted from an entities' taxes, reflecting a percentage of an amount invested in certain assets spread over the useful life of those assets; includes deferred investment tax credits.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

+ Details

Name:	us-gaap_InvestmentTaxCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 49
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-49

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-18

+ Details

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

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

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=tep_RoadrunnerReserveIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=tep_RoadrunnerReserveIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

NATURE OF OPERATIONS AND FINANCIAL STATEMENT PRESENTATION (Narrative) (Details) customer in Thousands, $ in Thousands		1 Months Ended					3 Months Ended		9 Months Ended
	Oct. 01, 2026 USD ($)	Jul. 31, 2026 USD ($)	Jun. 30, 2026 USD ($)	Apr. 30, 2026 USD ($)	Dec. 31, 2025 USD ($)	Jul. 31, 2025 USD ($)	Sep. 30, 2026 USD ($) customer	Sep. 30, 2025 USD ($)	Sep. 30, 2026 USD ($) mi² customer operatingSegment	Sep. 30, 2025 USD ($)
Public Utilities, General Disclosures [Line Items]
Number of retail customers \| customer							459		459
Area in which company generates transmits and distributes electricity to retail electric customers (sq miles) \| mi²									1,155
Number of operating segments \| operatingSegment									1
Operations and maintenance expense, excluding customer funded expenses							$ 87,000	$ 91,000	$ 275,000	$ 261,000
Proceeds from sale of investment tax credit									91,830	0
PTC benefits							11,000	$ 9,000	18,000	$ 17,000
Roadrunner Reserve II
Public Utilities, General Disclosures [Line Items]
Investment tax credit			$ 130,000
Tax credit percentage			0.10
Sales of investment tax credits		$ 50,000
Proceeds from sale of investment tax credit		$ 46,000
Accumulated deferred investment tax credit							67,000		67,000
Valuation allowance							$ 2,000		$ 2,000
Roadrunner Reserve II \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Sales of investment tax credits	$ 40,000
Proceeds from sale of investment tax credit	$ 37,000
Roadrunner Reserve I
Public Utilities, General Disclosures [Line Items]
Investment tax credit						$ 98,000
Sales of investment tax credits				$ 49,000	$ 49,000
Proceeds from sale of investment tax credit				$ 46,000	$ 46,000