Regulation (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	0 Months Ended	27 Months Ended		0 Months Ended
	Mar. 31, 2013	May 01, 2012 2012 Texas Retail Rate Case	Sep. 30, 2011 2012 Texas Retail Rate Case	Mar. 31, 2013 PUCT	Nov. 21, 2012 NMPRC MW	Jan. 31, 2013 FERC	Apr. 25, 2012 PUCT Docket No. 40302	Aug. 03, 2012 PUCT Docket No. 40622
Reconcilable Fuel Expense			$ 356.5
Reduction in Annual Nonfuel Base Rate		15
Reduction in Depreciation Expense		4.1
Return on Equity		10.125%
Number of years rate case expenses amortized		2 years
Percent Increase (Decrease) In Fixed Fuel Factor							(18.50%)
Fuel over and under materiality threshold percentage				4.00%
Refund Payments Authorized								6.6
Number of Applications for Air Permit	2
Certificate of Convenience and Necessity To Construct Number of Transmission Projects	2
Purchase Power Agreement of Solar Photovoltaic Plants					50
Refund Related to Dispute						$ 1.9