Rate Matters (Details) (USD $)			1 Months Ended							3 Months Ended		1 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	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	Oct. 31, 2013 Federal Energy Regulatory Commission (FERC) FERC Orders	Aug. 31, 2013 Federal Energy Regulatory Commission (FERC) FERC Orders Factor	Mar. 31, 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	Apr. 30, 2014 Subsequent Event Public Utility Commission of Texas (PUCT) 2014 Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Net Amount			$ 52,700,000
Public Utilities, Requested Rate Increase (Decrease), Percentage			5.80%
Public Utilities, Requested Return on Equity, Percentage			10.40%			10.25%	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 Rate Increase (Decrease), Amended, Net Amount														48,100,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage														5.30%
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						32,500,000								76,900,000
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to resetting TCRF to zero														(12,900,000)
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to customer credit for gain on sale														(4,900,000)
Public Utilities, Requested base revenue increase (decrease) excluding fuel clause offsets, Amended														59,100,000
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to fuel offsets														(11,000,000)
Public Utilities, Requested increase (decrease) to rider revenue				13,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount							45,900,000
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, Approved Return on Equity, Percentage					9.96%
Public Utilities, Approved Equity Capital Structure, Percentage					53.89%
Public Utilities, Approved Rate Increase (Decrease) due to pension, Amount					2,400,000
Public utilities, portion of approved rate increase (decrease) to be recovered through rider revenue					18,100,000
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 Rate Increase (Decrease) due to return on equity, Amount					(1,200,000)
Public Utilities, approved rate increase (decrease) due to rider adjustment for renewable energy costs					6,000,000
Public Utilities, approved rate increase (decrease) due to base rate adjustment for renewable energy costs					(6,000,000)
Public Utilities, Approved Rate Increase (Decrease) due to other, Amount					(500,000)
Public Utilities, portion of approved rate increase (decrease) to be recovered in base revenue					12,700,000
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	77,036,000	75,355,000									44,500,000
Current year pre-tax earnings impact of regulatory proceedings										1,900,000
Public utilities, annual increase (decrease) in revenues resulting from regulatory proceeding												$ (6,000,000)	$ (4,000,000)