Accounting For Derivative Instruments, Trading Activities And Activities Hedging.

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Counterparties which are individually composed of total credit exposure Greater than.

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Credit exposure to other counterparties related to supply and hedging contracts.

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Credit exposure to other counterparties related to wholesale marketing and gas hedging activities.

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Derivative contract maturity period.

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Forward Power Purchases.

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Forward Power Sales.

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- Definition

Gas swaps.

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Impact of credit risk on fair value of derivatives.

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Number of counterparties.

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Power contracts.

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Recorded in Wholesale Sales.

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Total Sales and Purchases Not Resulting in Physical Delivery.

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44D

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Fair value of all liability derivatives designated as cash flow hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44D

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44D

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Recorded in Wholesales:
Forward Power Sales	$ 6	$ 19	$ 9	$ 25
Forward Power Purchases	(8)	(25)	(12)	(32)
Total Sales and Purchases Not Resulting in Physical Delivery	(2)	(6)	(3)	(7)
Derivatives with Credit-Risk related Contingent Features
Cash Collateral Posted					3
Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Textual) [Abstract]
Maximum impact of counterparty credit risk and own credit risk on the fair value of derivative asset contracts	0.1		0.1		0.1
UniSource Energy [Member]
Derivatives with Credit-Risk related Contingent Features
Net Liability	58		58
Cash Collateral Posted	0		0
Letters of Credit	8		8
Additional Collateral to Post if Contingent Features Triggered	52		52
Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Textual) [Abstract]
Liabilities related to cash flow hedges of UniSource Energy and TEP	14		14		12
Gas swaps, in GBtu	13,963		13,963		14,973
Power contracts, in GWh	3,647		3,647		4,807
Contract maturity settlement date	through the third quarter of 2015		through the third quarter of 2015
UNS ELECTRIC, INC. [Member]
Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Textual) [Abstract]
Credit exposure to other counterparties related to supply and hedging contracts	3		3
Number of counterparties	1		1
TEP [Member]
Derivatives with Credit-Risk related Contingent Features
Net Liability	21		21
Cash Collateral Posted	0		0
Letters of Credit	1		1
Additional Collateral to Post if Contingent Features Triggered	21		21
Accounting for Derivative Instruments, Trading Activities and Activities Hedging (Textual) [Abstract]
Liabilities related to cash flow hedges of UniSource Energy and TEP	14		14		12
Gas swaps, in GBtu	5,977		5,977		6,424
Power contracts, in GWh	964		964		1,144
Credit exposure to other counterparties related to wholesale marketing and gas hedging activities	$ 17		$ 17
Number of counterparties	5		5
Counterparties which are individually composed of total credit exposure	10.00%		10.00%
Contract maturity settlement date	through the third quarter of 2015		through the third quarter of 2015