Regulatory Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended						12 Months Ended			1 Months Ended		12 Months Ended										1 Months Ended	12 Months Ended
	Apr. 30, 2012	Dec. 31, 2012 Pending UNS Electric Rate Case [Member]	Apr. 30, 2012 2012 UNS Gas Rate Order [Member]	Jul. 31, 2012 UNS Electric [Member]	Jun. 30, 2012 UNS Electric [Member]	Sep. 30, 2010 UNS Electric [Member]	Dec. 31, 2012 UNS Electric [Member]	Dec. 31, 2011 UNS Electric [Member]	Jul. 31, 2011 UNS Electric [Member]	Sep. 30, 2010 UNS Electric [Member] 2010 UNS Electric Rate Order [Member]	Dec. 31, 2012 UNS Electric [Member] Pending UNS Electric Rate Case [Member]	Dec. 31, 2012 UNS Gas [Member] Btu	Dec. 31, 2011 UNS Gas [Member] Btu	Dec. 31, 2010 UNS Gas [Member]	Dec. 31, 2012 UNS Gas [Member] Maximum [Member]	Dec. 31, 2011 UNS Gas [Member] Maximum [Member]	Dec. 31, 2012 UNS Gas [Member] Minimum [Member]	Dec. 31, 2011 UNS Gas [Member] Minimum [Member]	Dec. 31, 2012 Tucson Electric Power Company [Member]	Dec. 31, 2011 Tucson Electric Power Company [Member]	Dec. 31, 2008 Tucson Electric Power Company [Member] TEP 2008 Rate Order [Member]	Jul. 31, 2012 Tucson Electric Power Company [Member] Pending TEP Rate Case [Member]	Dec. 31, 2012 Tucson Electric Power Company [Member] Maximum [Member]	Dec. 31, 2012 Tucson Electric Power Company [Member] Minimum [Member]
Regulatory Liabilities [Line Items]
Fuel rate included in base rate																					2.9
Average increase in base rates over TEP's previous base rates																					6.00%
Authorized rate of return			8.30%							8.30%	6.70%										8.00%
Original Cost Rate Base, Amount			$ 183							$ 169	$ 217										$ 1,000	$ 1,500
Rate of Return on Fair Value Increment of Rate Base											1.60%										5.60%	5.68%
Fair Value of Rate Base											286										1,500	2,300
Base rate increase requested																						15.00%
Revenue deficiency to be covered																						128
Requested rate of return											8.40%											7.74%
Authorized rate of return on fair value rate base			1.00%							1.30%												1.56%
Fair value increment of rate base	70	69				73																800
Base Rate increase approved by ACC	2.7
Percentage of increase over base rate	1.80%
Base Rate increase approved by ACC										4.00%
Base Rate increase approved										7
FERC approved actual purchase price of BMGS									63
Revenue-neutral rate reclassification from base power supply rate to non-fuel base rates									0.7
Base rate increase requested by ACC											7.5
Fair Value of Rate Base											4.60%
PGA factor adjustment restriction in a twelve-month period												More than $0.15 per therm in a twelve-month period
Gas is required to request approval of a surcredit when the billed PGA balance exceeds												10
Approved Purchased Gas Adjustor temporary surcredit												4.5
Over collected PGA bank balance on billed basis												10
Increase in over collected PGA bank balance on billed to customer basis												2
Purchased gas adjustor rate															0.6501	0.7296	0.5202	0.6593
Proposed collections from customers in 2013				7															36
Proposed investments in company-owned solar projects							5												28
Investment in solar project																			8
Potential earnings on solar investment projects in 2013																			4
Term period of long-term purchase power agreements							20 years												20 years
Percentage of Energy Efficiency Standards target retail savings on sales								1.25%					1.20%	0.50%						1.25%
Percentage of Energy Efficient Standards target cumulative retail savings on sales by 31, December 2020								22.00%					6.00%							22.00%
Requested Energy Efficiency performance incentive					1																		4	3
Reduction in retail therm sales required as per new Gas EE Standards												1,679,890	701,113
LFCR revenue															0.1
Renewable energy credits							2	1
Extraordinary after-tax gain/loss							6					19							48
After-tax loss in AOCI							$ 3					$ 3							$ 78