Rate Matters (Details) (USD $)	12 Months Ended			1 Months Ended	0 Months Ended	1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Sale of Texas Transmission Assets Facility	Jan. 07, 2014 Public Utility Commission of Texas (PUCT) 2014 Electric Rate Case Subsequent Event	Nov. 30, 2012 Public Utility Commission of Texas (PUCT) Electric Rate Case 2012	Jun. 30, 2013 Public Utility Commission of Texas (PUCT) Electric Rate Case 2012, Settlement Rates Effective May 1, 2013	Jun. 30, 2013 Public Utility Commission of Texas (PUCT) Electric Rate Case 2012, Settlement Rates Effective September 1, 2013	Nov. 30, 2013 Public Utility Commission of Texas (PUCT) Transmission Cost Recovery Factor (TCRF) Rider	Sep. 30, 2013 New Mexico Public Regulation Commission (NMPRC) 2014 Electric Rate Case	Aug. 31, 2013 New Mexico Public Regulation Commission (NMPRC) 2014 Electric Rate Case		Jun. 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	Aug. 31, 2013 New Mexico Attorney General (NMAG) 2014 Electric Rate Case		Feb. 28, 2014 Hearing Examiner 2014 Electric Rate Case Subsequent Event	Jan. 31, 2014 Hearing Examiner 2014 Electric Rate Case Subsequent Event	Dec. 31, 2013 Federal Energy Regulatory Commission (FERC) Sale of Texas Transmission Assets	Dec. 31, 2013 Federal Energy Regulatory Commission (FERC) Sale of Texas Transmission Assets Customers	Dec. 31, 2013 Federal Energy Regulatory Commission (FERC) Sale of Texas Transmission Assets Shareholders	Oct. 31, 2013 Federal Energy Regulatory Commission (FERC) Federal Energy Regulatory Commission (FERC) Orders	Aug. 31, 2013 Federal Energy Regulatory Commission (FERC) Federal Energy Regulatory Commission (FERC) Orders Factor	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, 2012 Federal Energy Regulatory Commission (FERC) Wholesale Electric Rate Complaint
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 Rate Increase (Decrease), Amount					81,500,000	90,200,000								45,900,000
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					63,700,000
Public Utilities, Adjustment requested by public utility to rate increase (decrease) related to fuel offsets					(11,000,000)
Public Utilities, Requested Return on Equity, Percentage					10.40%	10.65%				10.25%				10.65%
Public Utilities, Requested Rate Base, Amount					1,270,000,000	1,150,000,000								479,800,000
Public Utilities, Requested Equity Capital Structure, Percentage					53.89%	52.00%								53.89%
Public Utilities, Approved Rate Increase (Decrease), Amount							37,000,000	13,800,000
Public Utilities, Portion of requested rate increase (decrease) related to depreciation expense					16,000,000
Public Utilities, Number of months included in test year for rate filing						12 months
Public Utilities, Requested increase (decrease) to rider revenue									13,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount										32,500,000			43,300,000
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to the rate rider for renewable energy costs											(14,500,000)	[1]			(8,500,000)	[1]
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to revenue adjustments											(4,400,000)				(6,400,000)
Public Utilities, Adjustment recommended by third parties related to return on equity											(3,200,000)				(8,100,000)
Public Utilities, ROE recommended by third parties											9.80%				8.63%			9.73%
Public Utilities, Adjustment to requested rate increase (decrease) related to change in capital structure											(1,500,000)				(1,100,000)
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to reduced recovery for employee benefits											(2,800,000)				(1,800,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to reduced recovery for payroll expense											(100,000)				(100,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to gain on sale of assets											0				(1,700,000)
Public Utilities, Adjustment to requested rate increase (decrease) recommended by third parties related to fuel clause revenue											6,000,000				0
Public Utilities, Adjustment to requested rate increase (decrease) requested by third parties related to other costs											(5,000,000)				(6,600,000)
Public Utilities, Rate increase (decrease) recommended by third parties											17,800,000				9,000,000			14,700,000
Public Utilities, portion of rate increase (decrease) recommended by third parties to be recovered in base revenue											8,800,000				(6,000,000)
Public Utilities, portion of rate increase (decrease) recommended by third parties to be recovered in rider revenue											7,300,000				13,300,000
Public Utilities, portion of rate increase (decrease) recommended by third parties to be recovered in fuel cost adjustment revenue											1,700,000				1,700,000
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, Addition (reduction) to revised requested rate increase (decrease) recommended by third parties																		6,200,000
Public Utilities, Equity capital structure recommended by third parties																		53.89%
Public Utilities, rider revenue increase (decrease) recommended by third parties																	12,100,000
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
Current year pre-tax earnings impact of regulatory proceedings																					13,600,000		(36,000,000)
Public Utilities, Annual increase (decrease) in revenues resulting from regulatory proceeding																								(6,000,000)	(4,000,000)	(3,100,000)
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, Percentage																										9.15%
Public Utilities, Rate increase (decrease) requested by third parties																										(3,300,000)
Public Utilities, return on equity incentive related to transmission formula rates (in basis points)																										50
Number of substations included in purchase and sale agreement				2
Proceeds from sale of transmission assets	37,118,000	0	0																37,100,000
Public Utilities, Regulatory liabilities recognized for jurisdictional gain sharing																				$ 7,200,000

[1] Adjustments represent recommended deferrals, extended amortizations and moving costs from rider to fuel in base rates.