Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Tables)

6 Months Ended

Jun. 30, 2011

Accounting For Derivative Instruments Trading Activities And Activities Hedging (Tables) [Abstract]

Settlement of forward power purchase and sales contracts that did not result in physical delivery

	UniSource Energy and TEP
	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2011			2010			2011			2010
	-Millions of Dollars-
Recorded in Wholesale Sales:
Forward Power Sales	$	2		$	5		$	3		$	7
Forward Power Purchases		(3	)		(6	)		(4	)		(7	)
Total Sales and Purchases Not Resulting in Physical Delivery	$	(1	)	$	(1	)	$	(1	)	$	—

Unrealized gains and losses on energy contracts

	UniSource Energy						TEP
				Three Months Ended June 30,
	2011			2010			2011		2010
	-Millions of Dollars-
Decrease to Regulatory Assets	$	(3	)	$	(9	)	$	—	$	(6	)

	Six Months Ended June 30,
	2011			2010		2011			2010
	-Millions of Dollars-
Increase (Decrease) to Regulatory Assets	$	(10	)	$	4	$	(2	)	$	(3	)

Fair value of assets and liabilities related to energy derivatives

	UniSource Energy						TEP
	June 30,			December 31,			June 30,			December 31,
	2011			2010			2011			2010
	-Millions of Dollars-
Assets	$	14		$	15		$	4		$	3
Liabilities		(31	)		(42	)		(6	)		(7	)
Net Liabilities	$	(17	)	$	(27	)	$	(2	)	$	(4	)

Sum of the fair value of all derivative instruments under contracts with credit-risk related contingent features

	UniSource Energy		TEP
	June 30, 2011
	-Millions of Dollars-
Net Liability	$	65	$	35
Cash Collateral Posted		1		1
Letters of Credit		12		1
Additional Collateral to Post if Contingent Features Triggered		58		34