Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Taxes [Abstract]

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

The items comprising income tax expense are as follows:

Year ended December 31 (In millions)	2015			2014			2013
Provision (Benefit) for Current Income Taxes
Federal	$	—		$	—		$	—
State	(5.2		)	(4.5		)	4.3
Total Provision (Benefit) for Current Income Taxes	(5.2		)	(4.5		)	4.3
Provision for Deferred Income Taxes, net
Federal	98.8			160.0			154.4
State	4.5			18.2			(26.4		)
Total Provision for Deferred Income Taxes, net	103.3			178.2			128.0
Deferred Federal Investment Tax Credits, net	(0.7		)	(0.9		)	(2.0		)
Total Income Tax Expense	$	97.4		$	172.8		$	130.3

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	2015		2014		2013
Statutory Federal tax rate	35.0	%	35.0	%	35.0	%
Federal renewable energy credit (A)	(8.9	)	(6.7	)	(7.2	)
Remeasurement of state deferred tax liabilities	(0.8	)	0.4		(4.1	)
401(k) dividends	(0.7	)	(0.5	)	(0.5	)
Federal investment tax credits, net	(0.2	)	(0.2	)	(0.4	)
Income attributable to noncontrolling interest	—		—		(0.3	)
State income taxes, net of Federal income tax benefit	0.1		1.2		0.4
Uncertain tax positions	0.7		0.5		1.5
Amortization of net unfunded deferred taxes	0.9		0.6		0.6
Other	0.3		0.1		(0.1	)
Effective income tax rate	26.4	%	30.4	%	24.9	%

(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, 2015and2014, respectively, were as follows:

December 31 (In millions)				2014
Current Deferred Income Tax Assets
Net operating losses				$	158.4
Accrued liabilities				15.6
Federal tax credits				12.4
Accrued vacation				4.4
Uncollectible accounts				0.6
Total Current Deferred Income Tax Assets				$	191.4
December 31 (In millions)	2015			2014
Non-Current Deferred Income Tax Liabilities, net
Accelerated depreciation and other property related differences	$	2,016.0		$	1,936.8
Investment in Enable Midstream Partners	623.4			641.8
Company pension plan	13.7			34.6
Income taxes refundable to customers, net	22.0			21.7
Regulatory asset	32.7			24.7
Bond redemption-unamortized costs	4.8			5.3
Derivative instruments	1.5			1.8
Federal tax credits	(184.4		)	(139.0		)
State tax credits	(106.7		)	(98.6		)
Net operating losses	(94.6		)	(19.8		)
Postretirement medical and life insurance benefits	(56.2		)	(56.4		)
Regulatory liabilities	(46.3		)	(58.0		)
Asset retirement obligations	(22.5		)	(21.4		)
Accrued liabilities	(14.0		)	—
Accrued vacation	(3.2		)	—
Deferred Federal investment tax credits	(0.9		)	(0.4		)
Uncollectible accounts	(0.5		)	—
Other	(6.6		)	(4.8		)
Non-Current Deferred Income Tax Liabilities, net	$	2,178.2		$	2,268.3

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

Following is a reconciliation of the Company’s total gross unrecognized tax benefits as of the years ended December 31, 2015, 2014, and 2013.

(In millions)	2015		2014		2013
Balance at January 1	$	10.5	$	7.8	$	—
Tax positions related to current year:
Additions	2.7		2.7		2.7
Tax positions related to prior years:
Additions	—		—		5.1
Balance at December 31	$	13.2	$	10.5	$	7.8

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
Net operating losses
State operating loss	$	695.5	$	25.6	2030
Federal operating loss	197.3		69.0		2030
Federal tax credits	184.4		184.4		2029
State tax credits
Oklahoma investment tax credits	127.8		83.0		N/A
Oklahoma capital investment board credits	7.3		7.3		N/A
Oklahoma zero emission tax credits	24.3		16.4		2020