Regulatory Matters - Summary of Authorized 2010-2012 RES Programs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
UNS Electric [Member]
Regulatory Matters [Line Items]
Investment in Company Owned Solar Projects	$ 5	$ 5
Return on Investment for Company Owned Solar Projects	1
Program Budget	8	8	9
Tucson Electric Power Company [Member]
Regulatory Matters [Line Items]
Investment in Company Owned Solar Projects	28	28	14
Return on Investment for Company Owned Solar Projects	2	1
Program Budget	$ 30	$ 36	$ 44	$ 12	$ 12