Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

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.

December 31 (In millions)	2019		2018
REGULATORY ASSETS
Current:
Fuel clause under recoveries	$	39.5	$	2.0
Production tax credit rider over credit (A)	1.7		6.9
Oklahoma demand program rider under recovery (A)	—		6.4
Other (A)	7.5		3.2
Total current regulatory assets	$	48.7	$	18.5
Non-current:
Benefit obligations regulatory asset	$	167.2	$	188.2
Deferred storm expenses	65.5		36.5
Sooner Dry Scrubbers	20.6		4.5
Smart Grid	18.4		25.6
Unamortized loss on reacquired debt	10.6		11.4
Arkansas deferred pension expenses	8.0		6.8
Pension tracker	2.3		—
Other	13.4		12.8
Total non-current regulatory assets	$	306.0	$	285.8
REGULATORY LIABILITIES
Current:
Reserve for tax refund and interim surcharge (B)	$	12.7	$	15.4
Fuel clause over recoveries	4.8		0.3
SPP cost tracker over recovery (B)	2.6		16.8
Oklahoma demand program rider over recovery (B)	2.0		—
Transmission cost recovery rider over recovery (B)	—		2.7
Other (B)	6.9		1.4
Total current regulatory liabilities	$	29.0	$	36.6
Non-current:
Income taxes refundable to customers, net	$	899.2	$	937.1
Accrued removal obligations, net	318.5		308.1
Pension tracker	—		18.7
Other	5.8		6.8
Total non-current regulatory liabilities	$	1,223.5	$	1,270.7

(A)Included in Other Current Assets in the Balance Sheets.

(B)Included in Other Current Liabilities in the Balance 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: 

December 31 (In millions)	2019		2018
Pension Plan and Restoration of Retirement Income Plan:
Net loss	$	160.5	$	185.3
Postretirement Benefit Plans:
Net loss	23.3		25.6
Prior service cost	(16.6)		(22.7)
Total	$	167.2	$	188.2

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

The following amounts in the benefit obligations regulatory asset at December 31, 2019 are expected to be recognized as components of net periodic benefit cost in 2020: 

(In millions)
Pension Plan and Restoration of Retirement Income Plan:
Net loss	$	11.4
Postretirement Benefit Plans:
Net loss	2.8
Prior service cost	(6.1)
Total	$	8.1

Schedule of Jointly Owned Utility Plants [Table Text Block]

The tables below present 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 the Statements of Income.

December 31, 2019 (In millions)	Percentage Ownership		Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
McClain Plant (A)	77	%	$	254.4	$	83.5	$	170.9
Redbud Plant (A)(B)	51	%	$	529.9	$	159.0	$	370.9

(A)Construction work in progress was $0.2 million and $1.4 million for the McClain and Redbud Plants, respectively.

(B)This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million.

December 31, 2018 (In millions)	Percentage Ownership		Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
McClain Plant (A)	77	%	$	227.2	$	78.2	$	149.0
Redbud Plant (A)(B)	51	%	$	493.9	$	145.3	$	348.6

(A)Construction work in progress was $0.2 million and $0.9 million for the McClain and Redbud Plants, respectively.

(B)This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 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: 

December 31, 2019 (In millions)	Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
Distribution assets	$	4,468.6	$	1,381.1	$	3,087.5
Electric generation assets (A)	4,838.6		1,601.0		3,237.6
Transmission assets (B)	2,901.1		565.5		2,335.6
Intangible plant	225.2		145.4		79.8
Other property and equipment	473.1		175.1		298.0
Total property, plant and equipment	$	12,906.6	$	3,868.1	$	9,038.5

(A)This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million.

(B)This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.8 million.

December 31, 2018 (In millions)	Total Property, Plant and Equipment		Accumulated Depreciation		Net Property, Plant and Equipment
Distribution assets	$	4,229.4	$	1,324.5	$	2,904.9
Electric generation assets (A)	4,657.2		1,572.8		3,084.4
Transmission assets (B)	2,846.7		534.2		2,312.5
Intangible plant	187.6		135.1		52.5
Other property and equipment	444.2		160.8		283.4
Total property, plant and equipment	$	12,365.1	$	3,727.4	$	8,637.7

(A)This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million.  

(B)This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.7 million.

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

The following table summarizes changes to OG&E's asset retirement obligations during the years ended December 31, 2019 and 2018.

(In millions)	2019		2018
Balance at January 1	$	83.9	$	75.1
Accretion expense	1.0		3.4
Revisions in estimated cash flows (A)	(2.4)		6.8
Liabilities settled (B)	(9.0)		(1.4)
Balance at December 31	$	73.5	$	83.9

(A)Assumptions changed related to the estimated cost of the removal of wind turbine assets and asbestos removal at OG&E's generating facilities.

(B)Asset retirement obligations were settled for asbestos removal and for the closure of an ash pond at OG&E's generating facilities.