Total number of shares awarded but not yet issued.

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- Definition

Percentage of performance share awards based on cumulative net Income.

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- Definition

Percentage of performance share awards based on total shareholder return.

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- Definition

Performance period for performance share awards.

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- Definition

Share-Based Compensation Awards Granted, Shares.

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- Definition

Share Based Compensation Plans Textuals Abstract.

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- Definition

Represents the expense recognized during the period arising from share-based compensation arrangements (for example, shares of stock, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph 64
-Subparagraph b

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph g(1)

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14
-Section F

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As of the latest balance-sheet date presented, the total compensation cost related to outstanding, nonvested share-based compensation awards not yet recognized (will be charged against earnings as services are performed or other vesting criteria are met).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph h

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- Definition

General descriptive information regarding an arrangement under which employees and directors receive (a) awards of equity shares, equity share options, or other equity instruments or (b) the entity incurs liabilities to them (1) in amounts based, at least in part, on the price of the entity's shares or other equity instruments or (2) that require or may require settlement by issuance of the entity's shares. Such an arrangement is usually provided to employees and directors to compensate them, provide performance incentives to them, and to attract or retain their services. May also include pertinent information particular to a plan that is not elsewhere specified in the taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph 64, 65

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph a

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- Definition

The weighted average fair value at grant for nonvested share-based awards issued during the period on other than stock option plans (for example, phantom stock plan, stock appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(2)(c)

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph c(1)

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- Definition

The maximum number of shares originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the share-based compensation plan. As stock options and equity instruments other than options are awarded to participants, the shares remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph a

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Share-Based Compensation Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		1 Months Ended			6 Months Ended		1 Months Ended				3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Mar. 31, 2011 Monte Carlo Simulation [Member] Performance Share [Member] Officer [Member]	Mar. 31, 2011 Cumulative Net Income [Member]	Mar. 31, 2011 Cumulative Net Income [Member] Performance Share [Member] Officer [Member]	Jun. 30, 2011 Cumulative Net Income [Member] Performance Share [Member] Officer [Member]	May 31, 2011 Omnibus Stock and Incentive Plan [Member]	May 31, 2011 Restricted Stock Unit [Member]	Mar. 31, 2011 Performance Share [Member]	Mar. 31, 2011 Performance Share [Member] Officer [Member]	May 31, 2011 Director [Member]	Jun. 30, 2011 TEP [Member]	Jun. 30, 2010 TEP [Member]	Jun. 30, 2011 TEP [Member]	Jun. 30, 2010 TEP [Member]
Share-Based Compensation Plans (Textuals) [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized									1,200,000
Share-Based Compensation Awards Granted, Shares												80,440	14,655
Restricted stock units granted, fair value, per share						$ 36.58						$ 33.73	$ 37.53
Share-based compensation arrangement by share-based payment award, description										The restricted stock units vest in one year or immediately upon death, disability, or retirement. Compensation expense equal to the fair market value on the grant date is recognized over the vesting period. Fully vested but undistributed stock unit awards accrue dividend equivalent stock units based on the fair market value of common shares on the date the dividend is paid. In the January following the year the person is no longer a director, common stock shares will be issued for the vested stock units.	80,440 performance share awards to officers. Half of the performance share awards had a grant date fair value, based on a Monte Carlo simulation, of $33.73 per share. Those awards will be paid out in shares of UniSource Energy Common Stock based on a comparison of UniSource Energy’s cumulative Total Shareholder Return to that of the Edison Electric Institute Index during the performance period of January 1, 2011 through December 31, 2013. The remaining half had a grant date fair value of $36.58 per share and will be paid out in shares of UniSource Energy Common Stock based on cumulative net income for the three-year period ended December 31, 2013. The performance shares vest based on the achievement of goals by the end of the performance period; any unearned awards are forfeited. Performance shares are eligible for dividend equivalents during the performance period.
Percentage of performance share awards based on total shareholder return					50.00%			50.00%
Percentage of performance share awards based on cumulative net Income							50.00%
Performance period for performance share awards							3
Share based compensation expense, net of amounts capitalized	$ 1	$ 1	$ 2	$ 1										$ 1	$ 1	$ 1	$ 1
Total unrecognized compensation expense on non-vested share-based compensation	$ 4		$ 4
Total number of shares awarded but not yet issued, including target performance based shares under the share-based compensation plans	1,000,000		1,000,000