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