Rate Matters (Details) (USD $)			1 Months Ended											6 Months Ended		1 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Apr. 30, 2014 Public Utility Commission of Texas (PUCT) 2014 Electric Rate Case	Jan. 31, 2014 Public Utility Commission of Texas (PUCT) 2014 Electric Rate Case	Nov. 30, 2013 Public Utility Commission of Texas (PUCT) Transmission Cost Recovery Factor (TCRF) Rider	Mar. 31, 2014 New Mexico Public Regulation Commission (NMPRC) 2014 Electric Rate Case	Sep. 30, 2013 New Mexico Public Regulation Commission (NMPRC) 2014 Electric Rate Case	Dec. 31, 2012 New Mexico Public Regulation Commission (NMPRC) 2014 Electric Rate Case	Jun. 30, 2014 Federal Energy Regulatory Commission (FERC) Wholesale Electric Rate Complaints	Jul. 31, 2013 Federal Energy Regulatory Commission (FERC) Wholesale Electric Rate Complaints	Apr. 30, 2012 Federal Energy Regulatory Commission (FERC) Wholesale Electric Rate Complaints	Oct. 31, 2013 Federal Energy Regulatory Commission (FERC) FERC Orders	Aug. 31, 2013 Federal Energy Regulatory Commission (FERC) FERC Orders Factor	Jun. 30, 2014 Federal Energy Regulatory Commission (FERC) FERC Orders	Dec. 31, 2013 Federal Energy Regulatory Commission (FERC) FERC Orders	Aug. 31, 2013 Federal Energy Regulatory Commission (FERC) FERC Orders, Settlement Impact Through May 31, 2015	Aug. 31, 2013 Federal Energy Regulatory Commission (FERC) FERC Orders, Settlement Impact Effective June 1, 2015	Jul. 31, 2014 Subsequent Event Public Utility Commission of Texas (PUCT) Transmission Cost Recovery Factor (TCRF) Rider
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Net Amount				$ 52,700,000
Public Utilities, Requested Rate Increase (Decrease), Percentage				5.80%
Public Utilities, Requested Rate Increase (Decrease), Amended, Net Amount			48,100,000
Public Utilities, Requested Return on Equity, Percentage				10.40%				10.65%
Public Utilities, Requested Rate Base, Amount				1,270,000,000				479,800,000
Public Utilities, Requested Equity Capital Structure, Percentage				53.89%				53.89%
Public Utilities, Portion of requested rate increase (decrease) related to depreciation expense				16,000,000
Public Utilities, Requested increase (decrease) to rider revenue					13,000,000
Public Utilities, Approved increase (decrease) to rider revenue																		4,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount								45,900,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							32,500,000
Public Utilities, Requested Return on Equity, Revised, Percentage							10.25%
Public utilities, portion of revised rate increase (decrease) related to base and fuel revenue.							20,900,000
Public utilities, portion of revised rate increase (decrease) related to rider revenue							12,100,000
Public utilities, portion of revised rate increase (decrease) related to other costs							(500,000)
Public Utilities, Approved Rate Increase (Decrease), Amount						33,100,000
Public Utilities, portion of approved rate increase (decrease) to be recovered in base revenue						12,700,000
Public utilities, portion of approved rate increase (decrease) to be recovered through rider revenue						18,100,000
Public Utilities, Approved Return on Equity, Percentage						9.96%
Public Utilities, Approved Equity Capital Structure, Percentage						53.89%
Public utilities, portion of approved rate increase (decrease) to be recovered through fuel clause adjustment						2,300,000
Public utilities, revised rate increase (decrease), fuel adjusted						34,800,000
Public Utilities, Approved adjustment to rate increase (decrease) due to return on equity						(1,200,000)
Public Utilities, Approved adjustment to rate increase (decrease) due to rider adjustment for renewable energy costs						6,000,000
Public Utilities, Approved adjustment to rate increase (decrease) due to base rate adjustment for renewable energy costs						(6,000,000)
Public Utilities, Approved adjustment to rate increase (decrease) due to other						(500,000)
Public Utilities, Base return on equity charged to customers through production formula rates, Percentage											10.25%
Public Utilities, Base return on equity charged to customers through transmission formula rates, Percentage											10.77%
Public Utilities, Base return on equity requested by customers to be charged through production formula rates, Percentage										9.15%
Public Utilities, Base return on equity requested by customers to be charged through transmission formula rates, Percentage										9.65%
Public Utilities, Number of steps to be used in discounted cash flow analysis									2
Number of components included in regulatory proceeding													2
Number of coincident peaks used as demand allocator, revised												3	3
Number of coincident peaks used as demand allocator, original													12
Other Liabilities, Current	78,628,000	75,355,000													44,500,000
Current year increase (decrease) to pre-tax earnings resulting from regulatory proceedings														(3,900,000)
Public utilities, annual increase (decrease) in revenues resulting from regulatory proceeding																$ (6,000,000)	$ (4,000,000)