Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2016

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:

(In millions)	March 31, 2016		December 31, 2015
Regulatory Assets
Current
Oklahoma demand program rider under recovery (A)	$	37.4	$	36.6
Other (A)	13.4		9.9
Total Current Regulatory Assets	$	50.8	$	46.5
Non-Current
Benefit obligations regulatory asset	$	240.0	$	242.2
Income taxes recoverable from customers, net	56.8		56.7
Smart Grid	43.6		43.6
Deferred storm expenses	30.9		27.6
Unamortized loss on reacquired debt	14.4		14.8
Other	17.1		17.3
Total Non-Current Regulatory Assets	$	402.8	$	402.2
Regulatory Liabilities
Current
Fuel clause over recoveries	$	63.2	$	61.3
Other (B)	3.7		7.5
Total Current Regulatory Liabilities	$	66.9	$	68.8
Non-Current
Accrued removal obligations, net	$	255.3	$	254.9
Pension tracker	22.0		17.7
Other (C)	1.0		1.0
Total Non-Current Regulatory Liabilities	$	278.3	$	273.6

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

(B) Included in Other Current Liabilities on the Condensed Consolidated Balance Sheets.

(C) Prior year amount of$1.0 millionreclassified from deferred other liabilities to Non-Current Regulatory Liabilities.

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

The following table summarizes changes to the Company's asset retirement obligations during thethree months endedMarch 31, 2016and2015.

	Three Months Ended March 31,
(In millions)	2016		2015
Balance at January 1	$	63.3	$	58.6
Accretion expense	0.7		0.6
Liabilities settled	—		(0.3		)
Balance at March 31	$	64.0	$	58.9

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

The following tables summarize changes in the components of accumulated other comprehensive income (loss) during the three months ended March 31, 2016 and 2015. All amounts below are presented net of tax.

	Pension Plan and Restoration of Retirement Income Plan					Postretirement Benefit Plans
(In millions)	Net loss			Prior service cost		Net loss		Prior service cost			Total
Balance at December 31, 2015	$	(39.2	)	$	0.1	$	2.5	$	1.5		$	(35.1	)
Amounts reclassified from accumulated other comprehensive income (loss)	0.8			—		—		(0.4		)	0.4
Balance at March 31, 2016	$	(38.4	)	$	0.1	$	2.5	$	1.1		$	(34.7	)

	Pension Plan and Restoration of Retirement Income Plan					Postretirement Benefit Plans
(In millions)	Net loss			Prior service cost		Net loss			Prior service cost			Total
Balance at December 31, 2014	$	(36.8	)	$	0.1	$	(8.0	)	$	3.3		$	(41.4	)
Amounts reclassified from accumulated other comprehensive income (loss)	0.4			—		0.2			(0.4		)	0.2
Balance at March 31, 2015	$	(36.4	)	$	0.1	$	(7.8	)	$	2.9		$	(41.2	)

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]

The following table summarizes significant amounts reclassified out of accumulated other comprehensive income (loss) by the respective line items in net income during the three months ended March 31, 2016 and 2015.

Details about Accumulated Other Comprehensive Income (Loss) Components	Amount Reclassified from Accumulated Other Comprehensive Income (Loss)						Affected Line Item in the Statement Where Net Income is Presented
	Three Months Ended March 31,
(In millions)	2016			2015
Amortization of defined benefit pension and restoration of retirement income plan items
Actuarial losses	$	(1.2	)	$	(1.2	)	(A)
	(0.4		)	(0.8		)	Tax benefit
	$	(0.8	)	$	(0.4	)	Net of tax
Amortization of postretirement benefit plan items
Actuarial losses	$	—		$	(0.4	)	(A)
Prior service cost	0.6			0.7			(A)
	0.6			0.3			Total before tax
	0.2			0.1			Tax expense
	$	0.4		$	0.2		Net of tax
Total reclassifications for the period	$	(0.4	)	$	(0.2	)	Net of tax

(A) These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost (see Note 10 for additional information).