Rate Matters - West Companies (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Oct. 22, 2015	Sep. 30, 2015	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 4,008,000	$ 3,215,000
Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		274,470	204,753
Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Construction Work in Progress		$ 681,991	$ 471,980
Louisiana 2012 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Louisiana Jurisdictional Share of the Turk Plant		29.00%
Net Increase in Louisiana Total Rates per the Settlement Agreement		$ 2,000
Base Rate Increase per the Settlement Agreement		85,000
Fuel Rate Decrease per the Settlement Agreement		$ 83,000
Return on Common Equity per the Settlement Agreement		10.00%
Reduction to Requested Revenue Increase as Approved in Stipulation Agreement		$ 3,000
Louisiana 2012 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Louisiana Jurisdictional Share of the Turk Plant		29.00%
Net Increase in Louisiana Total Rates per the Settlement Agreement		$ 2,000
Base Rate Increase per the Settlement Agreement		85,000
Fuel Rate Decrease per the Settlement Agreement		$ 83,000
Return on Common Equity per the Settlement Agreement		10.00%
Reduction to Requested Revenue Increase as Approved in Stipulation Agreement		$ 3,000
Louisiana 2014 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		5,000
Additional Requested Annual Increase		15,000
Requested Total Annual Increase		20,000
Amount of Interim Rates Implemented in January 2015 as Approved in Partial Settlement Agreement		15,000
Louisiana 2014 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		5,000
Additional Requested Annual Increase		15,000
Requested Total Annual Increase		20,000
Amount of Interim Rates Implemented in January 2015 as Approved in Partial Settlement Agreement		15,000
Louisiana 2015 Formula Rate Filing [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		14,000
Louisiana 2015 Formula Rate Filing [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		14,000
Oklahoma Base Rate Case - 2014 [Member]
Public Utilities, General Disclosures [Line Items]
Fourteen Months Of Revenues Beginning November 2014 Related To Advanced Metering Costs As Approved In Stipulation Agreement		24,000
2016 Revenues Related To Advanced Metering Costs As Approved In Stipulation Agreement		$ 27,000
Return On Common Equity For AFUDC And Factoring As Approved In Stipulation Agreement		9.85%
Oklahoma Base Rate Case - 2014 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Fourteen Months Of Revenues Beginning November 2014 Related To Advanced Metering Costs As Approved In Stipulation Agreement		$ 24,000
2016 Revenues Related To Advanced Metering Costs As Approved In Stipulation Agreement		$ 27,000
Return On Common Equity For AFUDC And Factoring As Approved In Stipulation Agreement		9.85%
Oklahoma Base Rate Case - 2015 [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		$ 137,000
Requested Base Rate Increase		89,000
Amount of Increased Depreciation Expense Requested		48,000
Amount of Increase Related to Environmental Controls		44,000
Amount Of Requested Increase Related To Environmental Consumable Costs In Fuel Adjustment Clause		$ 4,000
Requested Return on Equity		10.50%
Future Incremental Purchased Capacity and Energy Costs Related to Environmental Projects		$ 35,000
Oklahoma Base Rate Case - 2015 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Requested Annual Increase		137,000
Requested Base Rate Increase		89,000
Amount of Increased Depreciation Expense Requested		48,000
Amount of Increase Related to Environmental Controls		44,000
Amount Of Requested Increase Related To Environmental Consumable Costs In Fuel Adjustment Clause		$ 4,000
Requested Return on Equity		10.50%
Future Incremental Purchased Capacity and Energy Costs Related to Environmental Projects		$ 35,000
Oklahoma Base Rate Case - 2015 [Member] | Northeastern Plant, Unit 4 [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		94,000
Oklahoma Base Rate Case - 2015 [Member] | Northeastern Plant, Unit 4 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		94,000
Texas Base Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
2013 Reversal of Previously Recorded Regulatory Disallowances		114,000
Resulting Approved Base Rate Increase		52,000
Texas Base Rate Case [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
2013 Reversal of Previously Recorded Regulatory Disallowances		114,000
Resulting Approved Base Rate Increase		52,000
Texas Base Rate Case [Member] | Welsh Plant, Unit 2 [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		83,000
Texas Base Rate Case [Member] | Welsh Plant, Unit 2 [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		83,000
Welsh Plant, Units 1 and 3 - Environmental Projects [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		700,000
Construction Work in Progress		303,000
Remaining Contractual Construction Obligations		62,000
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		700,000
Construction Work in Progress		303,000
Remaining Contractual Construction Obligations		62,000
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Welsh Plant, Units 1 and 3 [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		529,000
Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Welsh Plant, Units 1 and 3 [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Property, Plant and Equipment, Net		529,000
Subsequent Event [Member] | Minimum [Member] | Oklahoma Base Rate Case - 2015 [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Recommended Increase to Annual Revenue and/or Rider	$ 10,000
Intervenor Recommended Return On Common Equity Range	8.75%
Intervenor Recommended Increase to Depreciation Expense	$ 23,000
Subsequent Event [Member] | Minimum [Member] | Oklahoma Base Rate Case - 2015 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Recommended Increase to Annual Revenue and/or Rider	$ 10,000
Intervenor Recommended Return On Common Equity Range	8.75%
Intervenor Recommended Increase to Depreciation Expense	$ 23,000
Subsequent Event [Member] | Maximum [Member] | Oklahoma Base Rate Case - 2015 [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Recommended Increase to Annual Revenue and/or Rider	$ 31,000
Intervenor Recommended Return On Common Equity Range	9.30%
Intervenor Recommended Increase to Depreciation Expense	$ 46,000
Subsequent Event [Member] | Maximum [Member] | Oklahoma Base Rate Case - 2015 [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Intervenor Recommended Increase to Annual Revenue and/or Rider	$ 31,000
Intervenor Recommended Return On Common Equity Range	9.30%
Intervenor Recommended Increase to Depreciation Expense	$ 46,000
Environmental Controls Projects [Member] | Oklahoma Base Rate Case - 2015 [Member] | Northeastern Plant, Unit 3 and Comanche Plant [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		219,000
Construction Work in Progress		162,000
Environmental Controls Projects [Member] | Oklahoma Base Rate Case - 2015 [Member] | Northeastern Plant, Unit 3 and Comanche Plant [Member] | Public Service Co Of Oklahoma [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		219,000
Construction Work in Progress		162,000
Mercury and Air Toxic Standards [Member] | Welsh Plant, Units 1 and 3 - Environmental Projects [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		410,000
Mercury and Air Toxic Standards [Member] | Welsh Plant, Units 1 and 3 - Environmental Projects [Member] | Southwestern Electric Power Co [Member]
Public Utilities, General Disclosures [Line Items]
Projected Capital Costs		$ 410,000