NATURE OF OPERATIONS AND FINANCIAL STATEMENT PRESENTATION (Nature of Operations) (Details) customer in Thousands	3 Months Ended
Mar. 31, 2020 mi² customer
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of retail customers \| customer	432
Area in which company generates transmits and distributes electricity to retail electric customers (square mile) \| mi²	1,155

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

No definition available.

Name:	tep_AreaInWhichSubsidiaryGeneratesTransmitsAndDistributesElectricityToRetailElectricCustomers
Namespace Prefix:	tep_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	duration