Accounting for Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
UNS Energy [Member]
Derivative [Line Items]
Liabilities related to cash flow hedges of UniSource Energy and TEP	$ 12	$ 14
Gas swaps, in GBtu	14,351	14,856
Power contracts, in GWh	2,228	3,147
UNS Energy [Member] | Tucson Electric Power Company [Member]
Derivative [Line Items]
Estimated reclassification to earnings	2
Credit risk impact on fair value of derivative asset contracts	0.5	0.5
Tucson Electric Power Company [Member]
Derivative [Line Items]
Liabilities related to cash flow hedges of UniSource Energy and TEP	12	14
Commodity derivatives final settlement period	Dec. 31, 2015
Gas swaps, in GBtu	6,158	6,855
Power contracts, in GWh	820	815
Credit exposure to other counterparties related to supply and hedging contracts	15
Number of counterparties	2
Counterparties which are individually composed of total credit exposure	10.00%
UNS Electric [Member]
Derivative [Line Items]
Credit exposure to other counterparties related to supply and hedging contracts	1
UNS Gas [Member]
Derivative [Line Items]
Credit exposure to other counterparties related to supply and hedging contracts	$ 1