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. 31, 2013 MW	Dec. 31, 2013 TUCSON ELECTRIC POWER COMPANY MW	Dec. 31, 2013 UNS Electric [Member] MW	Jun. 30, 2014 Letter of Credit [Member]
Unusual or Infrequent Item [Line Items]
Planned Purchase of Gas-Fired Generation Facility	$ 219	$ 164	$ 55
Generating capacity of plant in MW	550	413	137
Percentage of ownership in Generating Unit		75.00%	25.00%
Guaranty Liabilities				$ 15

This item represents a non-contingent liability for the fair value of an obligation to stand ready to perform over the term of a guaranty issued in the event that specified triggering events or conditions occur.

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