Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Details 2) (Energy Derivative [Member], USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
TEP [Member]
Fair value of assets and liabilities related to energy derivatives
Assets	$ 4	$ 3
Liabilities	(6)	(7)
Net Liabilities	(2)	(4)
UniSource Energy [Member]
Fair value of assets and liabilities related to energy derivatives
Assets	14	15
Liabilities	(31)	(42)
Net Liabilities	$ (17)	$ (27)

Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 205G

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
-Subparagraph a
-Clause 1

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- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

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- Definition

Fair value as of the balance sheet date of the assets less the liabilities of a derivative or group of derivatives.

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