Regulation (Narrative) (Details) (USD $)	0 Months Ended		3 Months Ended		6 Months Ended	12 Months Ended			27 Months Ended					0 Months Ended	12 Months Ended	56 Months Ended	12 Months Ended
	Dec. 09, 2011 Decimals	Nov. 22, 2011	Mar. 31, 2012	Mar. 31, 2011	Jun. 30, 2010	Apr. 30, 2013	Mar. 31, 2012	Mar. 31, 2011	Sep. 30, 2011	Mar. 29, 2012	Mar. 28, 2012	Nov. 01, 2011	Jul. 02, 2010	Dec. 09, 2011 Solar Power Generation Projects mW	Dec. 31, 2011 Tucson Electric Power Company TEP Transmission Agreement, per Judgement Maximum mW	Sep. 30, 2010 Tucson Electric Power Company TEP Transmission Agreement, per Settlement	Dec. 31, 2011 Tucson Electric Power Company TEP Transmission Agreement, per Settlement Maximum mW	Dec. 31, 2011 Tucson Electric Power Company Two TEP Transmission Agreements, 2011 Maximum mW	Mar. 29, 2012 NMPRC	Mar. 28, 2012 NMPRC	Oct. 13, 2011 NMPRC	Nov. 15, 2011 NMPRC Revolving Credit Facility Expiring September 2016	Mar. 29, 2012 FERC	Oct. 13, 2011 FERC
Annual non-fuel base rate increase													$ 17,150,000
Customer's percentage of off-system sales margins					90.00%
Retained percentage of off-system sales margins					75.00%								10.00%
Reconcilable Fuel Expense									356,500,000
Annual Nonfuel Base Rate reduction						15,000,000
Reduction In Depreciation Expense			20,518,000	20,936,000		4,100,000	80,913,000	82,663,000
Return on Equity						10.125%
Funding To Fund Decommissioning Fund						3,600,000
Reduction in fixed fuel factor, amount						30,000,000
Fuel over and under materiality threshold percentage			4.00%
Electric capacity, MW														2.6
Reduction in Return on the Energy Efficiency Expenses		2.00%
Certificate of Convenience and Necessity To Construct Number of Solar Power Gerneration Projects	5
Transmission capacity, MW															200		170	40
Number of Transmission Capacity Agreements												2
Electrical Transmission Revenue Including Interest																5,400,000
Electrical transmission revenue shared with customers					700,000
Percentage of electrical transmission revenue					25.00%
Line of Credit Facility																					200,000,000			200,000,000
Debt Instrument, Unused Borrowing Capacity, Amount																					300,000,000			300,000,000
Line of Credit Facility, Maximum Borrowing Capacity																					300,000,000			300,000,000
Line of Credit Facility, Current Borrowing Capacity										$ 300,000,000	$ 200,000,000								$ 300,000,000	$ 200,000,000		$ 200,000,000	$ 300,000,000