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NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Additional Information) (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended 12 Months Ended
Dec. 31, 2011
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2013
TUCSON ELECTRIC POWER COMPANY
sqmi
Dec. 31, 2013
UNS Electric
Dec. 31, 2013
UNS Gas
Dec. 31, 2013
Millennium Energy Holdings [Member]
Dec. 31, 2013
Springerville Unit 1 [Member]
Dec. 31, 2013
Springerville Common Facilities [Member]
Nature Of Business And Summary Of Significant Accounting Policies [Line Items]                  
Percentage of TEP owned by UNS Energy   100.00%              
Percentage Of Subsidiary In Companys Asset       83.00%          
Retail customers       413,000 93,000 150,000      
Area in which subsidiary generates transmits and distributes electricity to retail electric customers       1,155          
Investments In Unregulated Businesses As Percentage Of Companys Assets             1.00%    
Restricted Cash and Cash Equivalents, Noncurrent   $ 2 $ 7            
Capitalized interest 3.30%                
Equity Method Investment, Ownership Percentage               14.00% 7.00%