Supplemental Cash Flow Information (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Reconciliation of Net Income to Net Cash Flows - Operating Activities follows
Net Income	$ 59,712	$ 55,665	$ 101,787	$ 101,732
Adjustments to Reconcile Net Income To Net Cash Flows from Operating Activities
Depreciation Expense	33,553	32,450	99,653	95,773
Amortization Expense	7,882	7,177	22,513	20,797
Depreciation and Amortization Recorded to Fuel and Other O&M Expense			4,513	4,025
Amortization of Deferred Debt-Related Costs Included in Interest Expense			3,185	2,672
Provision for Retail Customer Bad Debts			1,305	2,881
Use of Renewable Energy Credits for Compliance			4,669
Deferred Income Taxes			77,741	57,722
Deferred Tax Valuation Allowance			(73)	5,702
Pension and Postretirement Expense			15,903	14,626
Pension and Postretirement Funding			(25,998)	(20,927)
Allowance for Equity Funds used During Construction			(3,516)	(2,780)
Share-Based Compensation Expense			2,025	2,102
Excess Tax Benefit from Stock Options Exercised			(29)	(1,796)
CTC Revenue Refunded	(16,000)		(30,652)	(8,152)
Decrease to Reflect PPFAC/PGA Recovery Treatment			(5,174)	(34,260)
Gain on settlement of EL Paso electric dispute			(7,391)
Loss on Millenniums Investments			0	5,208
Changes in Assets and Liabilities which Provided (Used) Cash Exclusive of Changes Shown Separately:
Accounts Receivable			(22,495)	(36,929)
Materials and Fuel Inventory			(195)	12,691
Accounts Payable			9,507	6,834
Income Taxes			(11,870)	4,724
Interest Accrued			(3,063)	(3,633)
Taxes Other Than Income Taxes			17,048	18,855
Other			11,094	7,666
Net Cash Flows - Operating Activities			260,487	255,533
TEP [Member]
Reconciliation of Net Income to Net Cash Flows - Operating Activities follows
Net Income	53,912	59,704	83,773	98,135
Adjustments to Reconcile Net Income To Net Cash Flows from Operating Activities
Depreciation Expense	26,541	25,190	78,124	74,143
Amortization Expense	8,798	8,153	25,282	23,963
Depreciation and Amortization Recorded to Fuel and Other O&M Expense			3,280	2,837
Amortization of Deferred Debt-Related Costs Included in Interest Expense			1,866	1,534
Provision for Retail Customer Bad Debts			942	1,961
Use of Renewable Energy Credits for Compliance			4,280
Deferred Income Taxes			66,090	48,916
Pension and Postretirement Expense			14,113	12,979
Pension and Postretirement Funding			(23,453)	(19,174)
Allowance for Equity Funds used During Construction			(2,980)	(2,340)
Share-Based Compensation Expense			1,580	1,628
CTC Revenue Refunded			(30,652)	(8,152)
Decrease to Reflect PPFAC/PGA Recovery Treatment			(5,146)	(23,023)
Gain on settlement of EL Paso electric dispute			(7,391)
Changes in Assets and Liabilities which Provided (Used) Cash Exclusive of Changes Shown Separately:
Accounts Receivable			(35,481)	(45,706)
Materials and Fuel Inventory			144	11,889
Accounts Payable			16,030	13,774
Income Taxes			(13,792)	(2,186)
Interest Accrued			1,685	1,420
Taxes Other Than Income Taxes			16,541	17,772
Other			10,709	10,541
Net Cash Flows - Operating Activities			$ 205,544	$ 220,911