Employee Benefit Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Accrued benefit liability Included in pension and other postretirement benefits	$ 159,401,000	$ 139,356,000
Approximate percentage of net periodic benefit cost capitalized as cost of construction	20.00%
Long term rate of return on plan assets range over years	20 years
Percentage of variance	2
Impact of amendment on estimated future benefit payments	5,000,000
Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Estimated amortization of net loss	1,000,000
Amortization of prior service cost	1,000,000
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	24,000,000	24,000,000
Estimated amortization of net loss	9,000,000
Amortization of prior service cost	500,000
Level 3 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Index value percentage of real estate assets	87.00%	85.00%
Fair value measurements of pension plan assets	19,000,000	15,000,000	12,000,000
Minimum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentile used to provide a best-estimate 20 year range for long term rate of return on assets	25.00%
Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Percentile used to provide a best-estimate 20 year range for long term rate of return on assets	75.00%
VEBA Trust [Member] | Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of pension plan assets	7,000,000	5,000,000
VEBA Trust [Member] | Other Postretirement Benefits [Member] | Fixed Income [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of pension plan assets	3,000,000	3,000,000
VEBA Trust [Member] | Other Postretirement Benefits [Member] | Equity Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of pension plan assets	4,000,000	2,000,000
Tucson Electric Power Company [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Accrued benefit liability Included in pension and other postretirement benefits	149,718,000	130,660,000
Matching contribution to plans	5,000,000	5,000,000	4,000,000
Tucson Electric Power Company [Member] | Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	5,000,000	5,000,000
Tucson Electric Power Company [Member] | Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	20,000,000	20,000,000
Tucson Electric Power Company [Member] | VEBA Trust [Member] | Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension plan contributions	3,000,000	2,000,000	2,000,000
UNS Gas and UNS Electric [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Pension benefit obligations	23,000,000	18,000,000
Pension benefit plan assets	14,000,000	10,000,000
UNS Gas and UNS Electric [Member] | 2013 Through 2017 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Expected annual pension and postretirement benefits to be made	2,000,000
UNS Gas and UNS Electric [Member] | 2018 Through 2022 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Expected annual pension and postretirement benefits to be made	9,000,000
UNS Gas and UNS Electric [Member] | Other Postretirement Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Accrued benefit liability Included in pension and other postretirement benefits	1,000,000	1,000,000
Postretirement benefit liability	1,000,000	1,000,000
Period for expected annual pension and post retirement benefits to be made	2018 through 2022
UNS Gas and UNS Electric [Member] | Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Accrued benefit liability Included in pension and other postretirement benefits	9,000,000	8,000,000
Period for expected annual pension and post retirement benefits to be made	2013 through 2017
UNS Gas and UNS Electric [Member] | Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Matching contribution to plans	1,000,000	1,000,000	1,000,000
UES Plan [Member] | Level 2 [Member] | Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value measurements of pension plan assets	$ 14,000,000	$ 10,000,000