PLANNED PURCHASE OF GAS-FIRED GENERATION FACILITY (Additional Information) (Details) (Entegra, Gila River Generating Station Unit 3 [Member], USD $) In Millions, unless otherwise specified	Dec. 23, 2013 MW
Unusual or Infrequent Item [Line Items]
Planned Purchase of Gas-Fired Generation Facility	$ 219
Generating capacity of plant in MW	550
TUCSON ELECTRIC POWER COMPANY
Unusual or Infrequent Item [Line Items]
Planned Purchase of Gas-Fired Generation Facility	164
Generating capacity of plant in MW	413
Percentage of ownership in Generating Unit	75.00%
UNS ELECTRIC, INC.
Unusual or Infrequent Item [Line Items]
Planned Purchase of Gas-Fired Generation Facility	$ 55
Generating capacity of plant in MW	137
Percentage of ownership in Generating Unit	25.00%