Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Details 1) (Energy Derivative [Member], USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
TEP [Member]
Unrealized gains and losses on energy contracts
Increase (Decrease) to Regulatory Assets	$ (1)	$ (1)	$ (3)	$ (4)
UniSource Energy [Member]
Unrealized gains and losses on energy contracts
Increase (Decrease) to Regulatory Assets	$ 2	$ 6	$ (7)	$ 10