Rate Matters, SPS (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Nov. 30, 2012 Public Utility Commission of Texas (PUCT) [Member] 2012 Electric Rate Case [Member]	Dec. 31, 2012 New Mexico Public Regulation Commission (NMPRC) [Member] 2012 Electric Rate Case [Member]	Apr. 30, 2012 Federal Energy Regulatory Commission (FERC) [Member] Wholesale Electric Rate Complaint [Member]
Rate Matters [Abstract]
Entity's requested rate increase (decrease)	$ 90.2	$ 45.9
Number of months included in test year for rate filing (in months)	12 months
Entity's requested return on equity (in hundredths)	10.65%	10.65%
Entity's rate base in requested rate increase (decrease)	1,150.0	479.8
Entity's requested equity ratio percent (in hundredths)	52.00%	53.89%
Entity's base return on equity charged to Golden Spread Electric Cooperative, Inc. through production formula rates (in hundredths)			10.25%
Entity's base return on equity charged to Golden Spread Electric Cooperative, Inc. through transmission formula rates (in hundredths)			10.77%
Entity's base return on equity requested by Golden Spread Electric Cooperative, Inc. (in hundredths)			9.15%
Golden Spread Electric Cooperative, Inc.'s original requested amount of increase (decrease) to existing rates			$ (3.3)
Entity's basis point incentive added to base return on equity for transmission formula rates (in hundredths)			0.50%