Income Taxes (Details) $ in Millions	9 Months Ended
Sep. 30, 2015 USD ($)
Valuation Allowance Excess Tax Basis Of Stock Over Book Value	$ 165
Valuation Allowance Deferred Tax Assets Realized	$ 221
Income Taxes (Textuals) [Abstract]
Pre-2016 TX Income/Franchise Tax Rate	0.95%
New TX Income/Franchise Tax Rate	0.75%
Anticipated TX Income/Franchise Tax Rate	1.00%
Public Service Co Of Oklahoma [Member]
Income Taxes (Textuals) [Abstract]
Pre-2016 TX Income/Franchise Tax Rate	0.95%
New TX Income/Franchise Tax Rate	0.75%
Anticipated TX Income/Franchise Tax Rate	1.00%
Southwestern Electric Power Co [Member]
Income Taxes (Textuals) [Abstract]
Pre-2016 TX Income/Franchise Tax Rate	0.95%
New TX Income/Franchise Tax Rate	0.75%
Anticipated TX Income/Franchise Tax Rate	1.00%

Texas income/franchise tax rate anticipated to take effect in 2016 until House Bill 32 passed in June 2015 allowing a reduced tax rate.

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Income Taxes.

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Texas income/franchise tax rate to take effect January 1, 2016 after reduction passed by House Bill 32 in June 2015.

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Texas original income/franchise tax rate before reduction passed by House Bill 32 in June 2015.

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Valuation allowance for unrealized capital losses recognizing only the portion of deferred tax assets that, more likely than not, will be realized.

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Valuation allowance attributable to unrealized capital loss associated with the excess tax basis of the stock over the book value of an investment.

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