NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Summary of Average Annual Depreciation Rates for All Utility Plants) (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
TUCSON ELECTRIC POWER COMPANY
Public Utility, Property, Plant and Equipment [Line Items]
Average annual depreciation rate	3.16%	3.22%	3.14%
UNS Electric
Public Utility, Property, Plant and Equipment [Line Items]
Average annual depreciation rate	3.94%	3.99%	4.02%
UNS Gas
Public Utility, Property, Plant and Equipment [Line Items]
Average annual depreciation rate	2.63%	2.69%	2.84%