Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
UniSource Energy [Member]
Unrealized losses on Derivative activities, Net-of-Tax
Net After-Tax Unrealized Losses	$ 2	$ 3	$ 3	$ 8
TEP [Member]
Unrealized losses on Derivative activities, Net-of-Tax
Net After-Tax Unrealized Losses	$ 2	$ 3	$ 3	$ 8