RELATED PARTY TRANSACTIONS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) facility	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Related Party Transaction, Due from (to) Related Parties [Abstract]
Receivables from Related Parties	$ 17,000	$ 9,000
Payables to Related Parties	2,000	5,000
Operating Revenues	1,592,586	1,424,741	$ 1,418,338
Supplemental Workforce, SES	605,606	515,030	505,796
Transmission Revenues, UNS Electric
Related Party Transaction, Due from (to) Related Parties [Abstract]
Transmission and Wholesale Revenue	11,000	9,000	7,000
Wholesale Revenues, UNS Electric
Related Party Transaction, Due from (to) Related Parties [Abstract]
Transmission and Wholesale Revenue	25,000	1,000	1,000
Control Area Services, UNS Electric
Related Party Transaction, Due from (to) Related Parties [Abstract]
Control Area Services and Corporate Services	6,000	4,000	4,000
Common Costs, UNS Energy Affiliates
Related Party Transaction, Due from (to) Related Parties [Abstract]
Common Costs, UNS Energy Affiliates	21,000	19,000	19,000
Supplemental Workforce, SES
Related Party Transaction, Due from (to) Related Parties [Abstract]
Supplemental Workforce, SES	0	14,000	15,000
Corporate Services, UNS Energy
Related Party Transaction, Due from (to) Related Parties [Abstract]
Corporate Services	$ 7,000	5,000	6,000
Intercompany allocation parent to subsidiary (in percentage)	85.00%
Management fee	$ 6,000	6,000	6,000
Corporate Services, UNS Energy Affiliates
Related Party Transaction, Due from (to) Related Parties [Abstract]
Corporate Services	3,000	4,000	4,000
Capacity Charges, UNS Gas
Related Party Transaction, Due from (to) Related Parties [Abstract]
Capacity Charges, UNS Gas	$ 0	0	1,000
Number of generation facilities | facility	1
Corporate Services, Fortis Affiliates
Related Party Transaction, Due from (to) Related Parties [Abstract]
Corporate Services	$ 0	1,000	0
Wholesale Revenues, UNS Electric
Related Party Transaction, Due from (to) Related Parties [Abstract]
Operating Revenues	1,000	0	$ 0
UNS Electric
Related Party Transaction, Due from (to) Related Parties [Abstract]
Receivables from Related Parties	8,000	6,000
UNS Energy
Related Party Transaction, Due from (to) Related Parties [Abstract]
Receivables from Related Parties	7,000	2,000
Payables to Related Parties	1,000	1,000
UNS Gas
Related Party Transaction, Due from (to) Related Parties [Abstract]
Receivables from Related Parties	2,000	1,000
Payables to Related Parties	1,000	0
SES
Related Party Transaction, Due from (to) Related Parties [Abstract]
Payables to Related Parties	$ 0	$ 4,000