Rate Matters, SPS (Details) - SPS			1 Months Ended							12 Months Ended
		Feb. 16, 2016 USD ($)	Jan. 31, 2016	Dec. 31, 2015 USD ($) MW	Nov. 30, 2015 USD ($)	Oct. 31, 2015 USD ($)	Aug. 31, 2015 matters complaint	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)
PUCT Proceeding - Texas 2015 Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 42,100,000				$ 42,100,000	$ 64,800,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									6.70%
Public Utilities, Requested Return on Equity, Percentage									10.25%
Public Utilities, Requested Rate Base, Amount									$ 1,600,000,000
Public Utilities, Requested Equity Capital Structure, Percentage									53.97%
Public Utilities, Additional Capital Investment									$ 392,000,000
NMPRC Proceeding - New Mexico 2015 Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount						$ 45,400,000
Public Utilities, Requested Return on Equity, Percentage						10.25%
Public Utilities, Requested Rate Base, Amount						$ 734,000,000
Public Utilities, Requested Equity Capital Structure, Percentage						53.97%
Public Utilities, Original Return on Equity, Percentage						9.96%
Public Utilities, Net Requested Increase Base Rates, Amount						$ 24,300,000
Public Utilities, Decrease In Base Fuel Revenues						21,100,000
Public Utilities, Base Period Deficiency						19,700,000
Public Utilities, Post Test Year Adjustment Related to Capital Expenditures						12,300,000
Public Utilities, Depreciation Expense						3,700,000
Public Utilities, SPP Transmission Expansion Plan						2,000,000
Public Utilities, ROE						1,600,000
Public Utilities, Rider Costs to be Recovered Through Base Rates, Amount						1,300,000
Public Utilities, Other Net						4,800,000
Public Utilities, Right to Use FTY Period										13 months
Global Settlement Agreement
Rate Matters [Abstract]
Public Utilities, Amount Recognized As a Reversal of Previously Recorded Reductions in Revenue					$ 7,900,000
Public Utilities, Base Return On Equity Charged to Customers Through Production Formula Rates, Percentage					10.00%
Public Utilities, Base Return On Equity Charged To Customers Through Transmission Formula Rates, Percentage					10.50%
Public Utilities, Number of Regulatory Matters Resolved | matters							9
Public Utilities, Number of Pending ROE Complaints Resolved | complaint							3
Sale of Texas Transmission Assets
Rate Matters [Abstract]
Public Utilities, Recognized Pre-Tax Gain After Impact Of Sharing With Retail Customers					$ 3,900,000
SPP Open Access Transmission Tariff Upgrade Costs
Rate Matters [Abstract]
Public Utilities, Accrual For Transmission Service Upgrades										$ 0
Administrative Law Judge | PUCT Proceeding - Texas 2015 Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Post Test Year Decrease Adjustments						(8,900,000)
Public Utilities, Decrease to Requested Return on Equity						(6,300,000)
Public Utilities, Decrease to Cost of Debt and Capital Structure						0
Public Utilities, Decrease to annual incentive compensation						(200,000)
Public Utilities, Decrease to O&M Expenses						(4,600,000)
Public Utilities, Decrease to Depreciation Expense						(2,700,000)
Public Utilities, Decrease to Property Taxes						(900,000)
Public Utilities, Decrease to Revenue Adjustments						(1,100,000)
Public Utilities, Decrease to Wholesale Load Reductions						0
Public Utilities, Decrease to Transmission Expansion Plan						(4,200,000)
Public Utilities, Increase Related To Other, Net						1,400,000
Public Utilities, Recommended Rate Increase (Decrease) (Including Case Expenses)						14,600,000
Public Utilities, Decrease Adjustment To Move Rate Case Expenses To Separate Docket						(200,000)
Public Utilities, Recommended Rate Increase (Decrease), Amount						14,400,000
Public Utilities, Impact Of New Depreciation Rules						(11,200,000)
Public Utilities, Earnings Impact						$ 3,200,000
Public Utility Commission of Texas (PUCT) | PUCT Proceeding - Texas 2015 Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Original Wholesale Load Reduction | MW				500
Public Utilities, Disallowance of Requested Wholesale Load Reduction | MW				300
Public Utilities, Approved Equity Capital Structure, Percentage				51.00%
Public Utilities, Post Test Year Decrease Adjustments				$ (8,900,000)
Public Utilities, Decrease to Requested Return on Equity				(6,300,000)
Public Utilities, Decrease to Cost of Debt and Capital Structure				(3,700,000)
Public Utilities, Decrease to annual incentive compensation				(300,000)
Public Utilities, Decrease to O&M Expenses				(4,600,000)
Public Utilities, Decrease to Depreciation Expense				(2,700,000)
Public Utilities, Decrease to Property Taxes				(900,000)
Public Utilities, Decrease to Revenue Adjustments				(1,600,000)
Public Utilities, Decrease to Wholesale Load Reductions				(11,500,000)
Public Utilities, Decrease to Transmission Expansion Plan				(4,200,000)
Public Utilities, Decrease related to other, net				(1,200,000)
Public Utilities, Approved Rate Increase (Decrease) (Including Case Expenses)				(3,800,000)
Public Utilities, Decrease Adjustment To Move Rate Case Expenses To Separate Docket				(200,000)
Public Utilities, Approved Rate Increase (Decrease), Amount				(4,000,000)
Public Utilities, Impact Of New Depreciation Rules				(11,200,000)
Public Utilities, Earnings Impact				$ (15,200,000)
Public Utilities, Approved Return on Equity, Percentage				9.70%
Golden Spread and Public Service Company of New Mexico | Global Settlement Agreement
Rate Matters [Abstract]
Public Utilities, Amount Refunded Due to Regulatory Settlement					$ 49,100,000
Subsequent Event | PUCT Proceeding - Texas 2016 Electric Rate Case
Rate Matters [Abstract]
Public Utilities, Requested Rate Increase (Decrease), Amount		$ 71,900,000
Public Utilities, Requested Rate Increase (Decrease), Percentage		14.40%
Public Utilities, Requested Return on Equity, Percentage		10.25%
Public Utilities, Requested Rate Base, Amount		$ 1,700,000,000
Public Utilities, Requested Equity Capital Structure, Percentage		53.97%
Public Utilities, Additional Capital Investment		$ 38,600,000
Public Utilities, Number of Days, Subsequent to Filing, Until Estimated Information Will Be Updated to Reflect Actual Results		45 days
Public Utilities, Increase (Decrease) to Jurisdictional Allocation Factors		$ 10,900,000
Public Utilities, ROE and Capital Structure		11,700,000
Public Utilities, Increase (Decrease) to Rate Case Expenses	[1]	4,500,000
Public Utilities, Increase Related To Other, Net		$ 6,200,000
Subsequent Event | Public Utility Commission of Texas (PUCT) | PUCT Proceeding - Texas 2015 Electric Rate Case
Rate Matters [Abstract]
Public Utilities, File of Motion for Rehearing, Period			20 days

[1] SPS anticipates rate case expenses, for this proceeding, to be separated from the request for consideration in a separate docket.