UTILITY PLANT AND JOINTLY-OWNED FACILITES (TEP's Interests in Jointly-Owned Generating Stations and Transmission Systems) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Public Utility, Property, Plant and Equipment [Line Items]
Plant in Service	$ 1,084
Construction Work in Progress	52
Accumulated Depreciation	607
Net Book Value	529
San Juan Units 1 and 2 [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Percentage of ownership in generating station	50.00%
Plant in Service	448
Construction Work in Progress	6
Accumulated Depreciation	230
Net Book Value	224
Navajo Units 1, 2, and 3 [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Percentage of ownership in generating station	7.50%
Plant in Service	152
Construction Work in Progress	1
Accumulated Depreciation	110
Net Book Value	43
Four Corners Units 4 and 5 [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Percentage of ownership in generating station	7.00%
Plant in Service	101
Construction Work in Progress	2
Accumulated Depreciation	75
Net Book Value	28
Luna Energy Facility [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Percentage of ownership in generating station	33.30%
Plant in Service	53
Construction Work in Progress	0
Accumulated Depreciation	2
Net Book Value	51
Transmission Facilities [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Plant in Service	330
Construction Work in Progress	43
Accumulated Depreciation	190
Net Book Value	$ 183