Fair Value Measurements (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Assets
Cash Equivalents	$ 33	$ 38
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	16	16
Collateral Posted		3
Energy Contracts	14	15
Total Assets	63	72
Liabilities
Total Liabilities	(47)	(54)
Net Total Assets and (Liabilities)	16	18
TEP [Member]
Assets
Cash Equivalents	14	21
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	16	16
Collateral Posted	0
Energy Contracts	3	3
Total Assets	33	40
Liabilities
Total Liabilities	(18)	(19)
Net Total Assets and (Liabilities)	15	21
TEP [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Cash Equivalents	14	21
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	0	0
Energy Contracts	0	0
Total Assets	14	21
Liabilities
Total Liabilities	0	0
Net Total Assets and (Liabilities)	14	21
TEP [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	0	0
TEP [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	0	0
TEP [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets
Cash Equivalents	0	0
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	16	16
Energy Contracts	0	0
Total Assets	16	16
Liabilities
Total Liabilities	(16)	(17)
Net Total Assets and (Liabilities)	0	(1)
TEP [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(12)	(10)
TEP [Member] \| Significant Other Observable Inputs (Level 2) [Member] \| Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(4)	(7)
TEP [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets
Cash Equivalents	0	0
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	0	0
Energy Contracts	3	3
Total Assets	3	3
Liabilities
Total Liabilities	(2)	(2)
Net Total Assets and (Liabilities)	1	1
TEP [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	0	0
TEP [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(2)	(2)
TEP [Member] \| Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(12)	(10)
TEP [Member] \| Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(6)	(9)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Cash Equivalents	33	38
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	0	0
Collateral Posted		0
Energy Contracts	0	0
Total Assets	33	38
Liabilities
Total Liabilities	0	0
Net Total Assets and (Liabilities)	33	38
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets
Cash Equivalents	0	0
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	16	16
Collateral Posted		3
Energy Contracts	1	0
Total Assets	17	19
Liabilities
Total Liabilities	(24)	(29)
Net Total Assets and (Liabilities)	(7)	(10)
Significant Other Observable Inputs (Level 2) [Member] \| Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(12)	(10)
Significant Other Observable Inputs (Level 2) [Member] \| Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(12)	(19)
Significant Unobservable Inputs (Level 3) [Member]
Assets
Cash Equivalents	0	0
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	0	0
Collateral Posted		0
Energy Contracts	13	15
Total Assets	13	15
Liabilities
Total Liabilities	(23)	(25)
Net Total Assets and (Liabilities)	(10)	(10)
Significant Unobservable Inputs (Level 3) [Member] \| Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	0	0
Significant Unobservable Inputs (Level 3) [Member] \| Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(23)	(25)
Interest Rate Swap [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	(12)	(10)
Energy Contracts [Member]
Liabilities
Energy Contracts & Interest Rate Swaps	$ (35)	$ (44)

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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