Fair Value Measurements (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Assets
Cash Equivalents	$ 30	$ 38
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	18	16
Collateral Posted	1	3
Energy Contracts	14	15
Total Assets	63	72
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	(44)	(54)
Net Total Assets and (Liabilities)	19	18
TEP [Member]
Assets
Cash Equivalents	9	21
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	18	16
Collateral Posted	1
Energy Contracts	4	3
Total Assets	32	40
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	(18)	(19)
Net Total Assets and (Liabilities)	14	21
TEP [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Cash Equivalents	9	21
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	0	0
Collateral Posted	0
Energy Contracts	0	0
Total Assets	9	21
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	18	16
Collateral Posted	1
Energy Contracts	0	0
Total Assets	19	16
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
Collateral Posted	0
Energy Contracts	4	3
Total Assets	4	3
TEP [Member] | Interest Rate Swap [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	10	10
TEP [Member] | Interest Rate Swap [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	0	0
TEP [Member] | Interest Rate Swap [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	10	10
TEP [Member] | Interest Rate Swap [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	0	0
TEP [Member] | Energy Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	8	9
TEP [Member] | Energy Contracts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	0	0
TEP [Member] | Energy Contracts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	5	7
TEP [Member] | Energy Contracts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	3	2
TEP [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	0	0
Net Total Assets and (Liabilities)	0	21
TEP [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	(15)	(17)
Net Total Assets and (Liabilities)	4	(1)
TEP [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	(3)	(2)
Net Total Assets and (Liabilities)	1	1
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Cash Equivalents	30	38
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	0	0
Collateral Posted	0	0
Energy Contracts	0	0
Total Assets	30	38
Interest Rate Swap [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	0	0
Energy Contracts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	0	0
Net Total Assets and (Liabilities)	30	38
Significant Other Observable Inputs (Level 2) [Member]
Assets
Cash Equivalents	0	0
Rabbi Trust Investments to support the Deferred Compensation and SERP Plans	18	16
Collateral Posted	1	3
Energy Contracts	1	0
Total Assets	20	19
Interest Rate Swap [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	10	10
Energy Contracts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	(12)	19
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	(22)	(29)
Net Total Assets and (Liabilities)	(2)	(10)
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	0
Energy Contracts	13	15
Total Assets	13	15
Interest Rate Swap [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	0	0
Energy Contracts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	(22)	25
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Total Liabilities	(22)	(25)
Net Total Assets and (Liabilities)	(9)	(10)
Interest Rate Swap [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	10	10
Energy Contracts [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Energy Contracts & Interest Rate Swaps	$ (34)	$ 44