Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2014

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Regulatory Assets and Liabilities [Table Text Block]

The following table is a summary of OG&E's regulatory assets and liabilities at:

December 31 (In millions)	2014		2013
Regulatory Assets
Current
Fuel clause under recoveries	$	68.3	$	26.2
Oklahoma demand program rider under recovery (A)	19.7		10.6
Crossroads wind farm rider under recovery (A)	—		4.7
Other (A)	9.1		7.3
Total Current Regulatory Assets	$	97.1	$	48.8
Non-Current
Benefit obligations regulatory asset	$	261.1	$	227.4
Income taxes recoverable from customers, net	56.1		56.5
Smart Grid	43.9		44.2
Deferred storm expenses	17.5		21.6
Unamortized loss on reacquired debt	16.1		11.8
Pension tracker	—		1.4
Other	16.8		16.2
Total Non-Current Regulatory Assets	$	411.5	$	379.1
Regulatory Liabilities
Current
Smart Grid rider over recovery (B)	$	12.5	$	16.7
Crossroads wind farm rider over recovery (B)	10.3		—
Other (B)	1.6		3.5
Total Current Regulatory Liabilities	$	24.4	$	20.2
Non-Current
Accrued removal obligations, net	$	248.1	$	227.7
Pension tracker	14.9		—
Deferred pension credits	—		6.5
Total Non-Current Regulatory Liabilities	$	263.0	$	234.2

(A) Included in Other Current Assets on theBalance Sheets.

(B) Included in Other Current Liabilities on theBalance Sheets.

Components of Benefit Obligation Regulatory Asset [Table Text Block]

The following table is a summary of the components of the benefit obligations regulatory asset at:

December 31 (In millions)	2014			2013
Pension Plan and Restoration of Retirement Income Plan
Net loss	$	196.7		$	178.4
Prior service cost	0.6			2.5
Postretirement Benefit Plans
Net loss	83.6			79.9
Prior service cost	(19.8		)	(33.4		)
Total	$	261.1		$	227.4

Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block]

The following amounts in the benefit obligations regulatory asset atDecember 31, 2014are expected to be recognized as components of net periodic benefit cost in2015: 

(In millions)
Pension Plan and Restoration of Retirement Income Plan
Net loss	$	12.7
Prior service cost	0.5
Postretirement Benefit Plans
Net loss	11.8
Prior service cost	(13.7		)
Total	$	11.3

Schedule of Jointly Owned Utility Plants [Table Text Block]

The table below presents OG&E's ownership interest in the jointly-owned McClain Plant and the jointly-owned Redbud Plant, and, as disclosed below, only OG&E's ownership interest is reflected in the property, plant and equipment and accumulated depreciation balances in these tables.  The owners of the remaining interests in the McClain Plant and the Redbud Plant are responsible for providing their own financing of capital expenditures.  Also, only OG&E's proportionate interests of any direct expenses of the McClain Plant and the Redbud Plant such as fuel, maintenance expense and other operating expenses are included in the applicable financial statement captions in theStatement of Income.

December 31, 2014 (In millions)	Percentage Ownership		Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
McClain Plant (A)	77	%	$	207.7	$	46.6	$	161.1
Redbud Plant (A)(B)	51	%	$	484.1	$	81.8	$	402.3

(A) Construction work in progress was$0.5 millionand$0.4 millionfor the McClain and Redbud Plants, respectively.

(B) This amount includes a plant acquisition adjustment of$148.3 millionand accumulated amortization of$34.3 million.

December 31, 2013 (In millions)	Percentage Ownership		Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
McClain Plant (A)	77	%	$	183.2	$	62.8	$	120.4
Redbud Plant (A)(B)	51	%	$	498.9	$	89.7	$	409.2

(A) Construction work in progress was$0.1 millionand$39.5 millionfor the McClain and Redbud Plants, respectively.

(B) This amount includes a plant acquisition adjustment of$148.3 millionand accumulated amortization of$28.8 million.

Property, Plant and Equipment [Table Text Block]

OG&E's property, plant and equipment and related accumulated depreciation are divided into the following major classes at:

December 31, 2014 (In millions)	Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
Distribution assets	$	3,559.5	$	1,086.7	$	2,472.8
Electric generation assets (A)	3,620.1		1,345.1		2,275.0
Transmission assets (B)	2,370.0		417.8		1,952.2
Intangible plant	67.6		31.1		36.5
Other property and equipment	330.0		125.0		205.0
Total property, plant and equipment	$	9,947.2	$	3,005.7	$	6,941.5

(A) This amount includes a plant acquisition adjustment of$148.3 millionand accumulated amortization of$34.3 million.

(B) This amount includes a plant acquisition adjustment of$3.3 millionand accumulated amortization of$0.4 million.

December 31, 2013 (In millions)	Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
Distribution assets	$	3,403.8	$	1,028.2	$	2,375.6
Electric generation assets (A)	3,551.0		1,306.1		2,244.9
Transmission assets (B)	2,163.7		385.0		1,778.7
Intangible plant	50.5		27.1		23.4
Other property and equipment	330.2		118.2		212.0
Total property, plant and equipment	$	9,499.2	$	2,864.6	$	6,634.6

(A) This amount includes a plant acquisition adjustment of$148.3 millionand accumulated amortization of$28.8 million.

(B) This amount includes a plant acquisition adjustment of$3.3 millionand accumulated amortization of$0.3 million.

Schedule of Change in Asset Retirement Obligation [Table Text Block]

The following table summarizes changes to OG&E's asset retirement obligations during theyears endedDecember 31, 2014and2013.

(In millions)	2014			2013
Balance at January 1	$	55.2		$	53.6
Liabilities settled	(0.8		)	—
Accretion expense	2.5			2.3
Revisions in estimated cash flows	1.7			(0.7		)
Balance at December 31	$	58.6		$	55.2