Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

The items comprising income tax (benefit) expense are as follows:

Year Ended December 31 (In millions)	2017			2016			2015
Provision (benefit) for current income taxes:
Federal	$	26.3		$	2.9		$	(17.5	)
State	(4.3		)	(5.3		)	(5.3		)
Total provision (benefit) for current income taxes	22.0			(2.4		)	(22.8		)
Provision for deferred income taxes, net:
Federal	100.0			99.8			117.0
State	19.9			17.2			11.3
Total provision for deferred income taxes, net	119.9			117.0			128.3
Deferred federal investment tax credits, net	(0.1		)	(0.2		)	(0.7		)
Total income tax expense	$	141.8		$	114.4		$	104.8

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

The following schedule reconciles the statutory tax rates to the effective income tax rate:

Year Ended December 31	2017		2016		2015
Statutory federal tax rate	35.0	%	35.0	%	35.0	%
State income taxes, net of federal income tax benefit	2.2		1.8		0.5
Amortization of net unfunded deferred taxes	0.9		0.8		0.9
Federal renewable energy credit (A)	(6.1	)	(8.2	)	(8.8	)
Other	(0.3	)	0.1		(0.1	)
Uncertain tax positions	—		0.1		0.7
Federal investment tax credits, net	—		(0.9	)	(0.2	)
Effective income tax rate	31.7	%	28.7	%	28.0	%

(A) Represents credits associated with the production from OG&E's wind farms.

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

The components of Deferred Income Taxes atDecember 31, 2017and2016were as follows:

December 31 (In millions)	2017			2016
Deferred income tax liabilities, net:
Accelerated depreciation and other property related differences	$	1,449.6		$	2,101.4
OG&E Pension Plan	28.4			48.0
Regulatory asset	18.9			34.4
Bond redemption-unamortized costs	2.6			4.3
Income taxes (recoverable from) refundable to customers, net	(244.3		)	24.1
Federal tax credits	(218.3		)	(209.3		)
State tax credits	(129.2		)	(102.6		)
Asset retirement obligations	(19.2		)	(24.5		)
Postretirement medical and life insurance benefits	(17.4		)	(34.3		)
Regulatory liabilities	(16.8		)	(34.6		)
Net operating losses	(11.2		)	(26.1		)
Other	(4.8		)	(16.7		)
Accrued liabilities	(3.8		)	(8.0		)
Accrued vacation	(1.4		)	(2.4		)
Deferred federal investment tax credits	(0.5		)	(0.8		)
Uncollectible accounts	(0.4		)	(0.6		)
Total deferred income tax liabilities, net	$	832.2		$	1,752.3

Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]

Following is a reconciliation of OG&E’s total gross unrecognized tax benefits as of the years ended December 31, 2017, 2016 and 2015.

(In millions)	2017		2016		2015
Balance at January 1	$	20.7	$	20.2	$	16.1
Tax positions related to current year:
Additions	—		0.5		4.1
Balance at December 31	$	20.7	$	20.7	$	20.2

Summary of Tax Credit Carryforwards [Table Text Block]

The following table summarizes these carry forwards:

(In millions)	Carry Forward Amount		Deferred Tax Asset		Earliest Expiration Date
State operating loss	$	250.5	$	11.2	2030
Federal tax credits	218.3		218.3		2029
State tax credits:
Oklahoma investment tax credits	128.2		101.3		N/A
Oklahoma capital investment board credits	8.5		8.5		N/A
Oklahoma zero emission tax credits	24.1		19.4		2020