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EMPLOYEE BENEFIT PLANS (Change in Projected Benefit Obligation and Plan Assets and Reconciliation of Funded Status) (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2013
UNS Gas and UNS Electric [Member]
Dec. 31, 2012
UNS Gas and UNS Electric [Member]
Dec. 31, 2013
Pension Benefits [Member]
Dec. 31, 2012
Pension Benefits [Member]
Dec. 31, 2011
Pension Benefits [Member]
Dec. 31, 2013
Pension Benefits [Member]
TUCSON ELECTRIC POWER COMPANY
Dec. 31, 2012
Pension Benefits [Member]
TUCSON ELECTRIC POWER COMPANY
Dec. 31, 2013
Pension Benefits [Member]
UNS Gas and UNS Electric [Member]
Dec. 31, 2012
Pension Benefits [Member]
UNS Gas and UNS Electric [Member]
Dec. 31, 2013
Other Retiree Benefits [Member]
Dec. 31, 2012
Other Retiree Benefits [Member]
Dec. 31, 2011
Other Retiree Benefits [Member]
Dec. 31, 2013
Other Retiree Benefits [Member]
TUCSON ELECTRIC POWER COMPANY
Dec. 31, 2012
Other Retiree Benefits [Member]
TUCSON ELECTRIC POWER COMPANY
Dec. 31, 2013
Other Retiree Benefits [Member]
UNS Gas and UNS Electric [Member]
Dec. 31, 2014
Scenario, Forecast [Member]
Pension Benefits [Member]
Dec. 31, 2014
Scenario, Forecast [Member]
Pension Benefits [Member]
TUCSON ELECTRIC POWER COMPANY
Funded Status And Amount Recognized In Balance Sheet And Statement Of Operations [Line items]                                      
Pension plan contributions         $ 23 $ 23   $ 22 $ 20     $ 6 $ 5   $ 6 $ 5      
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year                                   10 9
Pension benefit obligations         352 380 319     21 23 75 78 73     1    
Defined Benefit Plan, Fair Value of Plan Assets $ 323 $ 289 $ 16 $ 14 $ 323 $ 289 $ 245         $ 10 $ 7 $ 5