COMMITMENTS AND CONTINGENCIES (Mine Reclamation at Generation Facilities Not Operated by TEP) (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Four Corners
Jointly Owned Utility Plant Interests [Line Items]
Final mine reclamation liability	$ 2	$ 3
San Juan
Jointly Owned Utility Plant Interests [Line Items]
Final mine reclamation liability	$ 17	$ 23

Carrying amount as of the balance sheet date of the liability for remediation, site restoration, postclosure, monitoring commitments, or other exit costs associated with the sale, disposal or abandonment of a particular property resulting from unanticipated contamination of the assets.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.Y.Q4)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480102/450-20-S99-1

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