UTILITY PLANT AND JOINTLY-OWNED FACILITES (Utility Plant in Service by Company and Major Class) (Detail) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Plant in Service:
Total Plant in Service	$ 5,192,122,000		$ 5,005,768,000
Utility Plant under Capital Leases	638,000,000	[1]	583,000,000	[1]
Electricity Generation Plant, Non-Nuclear [Member]
Plant in Service:
Total Plant in Service	1,974,000,000		1,932,000,000
Electric Transmission Plant [Member]
Plant in Service:
Total Plant in Service	912,000,000		842,000,000
Electric Distribution Plant [Member]
Plant in Service:
Total Plant in Service	1,529,000,000		1,495,000,000
Gas Distribution Plant [Member]
Plant in Service:
Total Plant in Service	252,000,000		240,000,000
Gas Transmission Plant [Member]
Plant in Service:
Total Plant in Service	18,000,000		18,000,000
General Plant [Member]
Plant in Service:
Total Plant in Service	356,000,000		347,000,000
Software Costs [Member]
Plant in Service:
Total Plant in Service	142,000,000	[2],[3]	124,000,000	[2],[3]
Intangible Plant [Member]
Plant in Service:
Total Plant in Service	5,000,000		5,000,000
Electric Plant Held for Future Use [Member]
Plant in Service:
Total Plant in Service	4,000,000		3,000,000
TUCSON ELECTRIC POWER COMPANY
Plant in Service:
Total Plant in Service	4,467,667,000		4,348,041,000
Utility Plant under Capital Leases	638,000,000	[1]	583,000,000	[1]
TUCSON ELECTRIC POWER COMPANY | Electricity Generation Plant, Non-Nuclear [Member]
Plant in Service:
Total Plant in Service	1,889,000,000		1,847,000,000
TUCSON ELECTRIC POWER COMPANY | Electric Transmission Plant [Member]
Plant in Service:
Total Plant in Service	825,000,000		796,000,000
TUCSON ELECTRIC POWER COMPANY | Electric Distribution Plant [Member]
Plant in Service:
Total Plant in Service	1,298,000,000		1,271,000,000
TUCSON ELECTRIC POWER COMPANY | Gas Distribution Plant [Member]
Plant in Service:
Total Plant in Service	0		0
TUCSON ELECTRIC POWER COMPANY | Gas Transmission Plant [Member]
Plant in Service:
Total Plant in Service	0		0
TUCSON ELECTRIC POWER COMPANY | General Plant [Member]
Plant in Service:
Total Plant in Service	312,000,000		309,000,000
TUCSON ELECTRIC POWER COMPANY | Software Costs [Member]
Plant in Service:
Total Plant in Service	141,000,000	[2],[3]	123,000,000	[2],[3]
TUCSON ELECTRIC POWER COMPANY | Intangible Plant [Member]
Plant in Service:
Total Plant in Service	0		0
TUCSON ELECTRIC POWER COMPANY | Electric Plant Held for Future Use [Member]
Plant in Service:
Total Plant in Service	$ 3,000,000		$ 2,000,000

[1] In 2013, TEP entered into agreements to purchase certain Springerville Unit 1 leased interests. See Note 6.

[2] Unamortized computer software costs were $40 million for UNS Energy and $39 million for TEP as of December 31, 2013, and $36 million for UNS Energy and $35 million for TEP as of December 31, 2012.

[3] The amortization of computer software costs in UNS Energy’s and TEP's income statements was $14 million in 2013, $13 million in 2012, and $10 million in 2011.