Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

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)	2016			2015			2014
Provision (Benefit) for Current Income Taxes
Federal	$	—		$	—		$	—
State	(5.7		)	(5.2		)	(4.5		)
Total Provision (Benefit) for Current Income Taxes	(5.7		)	(5.2		)	(4.5		)
Provision for Deferred Income Taxes, net
Federal	126.0			98.8			160.0
State	28.0			4.5			18.2
Total Provision for Deferred Income Taxes, net	154.0			103.3			178.2
Deferred Federal Investment Tax Credits, net	(0.2		)	(0.7		)	(0.9		)
Total Income Tax Expense	$	148.1		$	97.4		$	172.8

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	2016		2015		2014
Statutory Federal tax rate	35.0	%	35.0	%	35.0	%
Federal renewable energy credit (A)	(6.8	)	(8.9	)	(6.7	)
Remeasurement of state deferred tax liabilities	0.9		(0.8	)	0.4
401(k) dividends	(0.6	)	(0.7	)	(0.5	)
Federal investment tax credits, net	(0.8	)	(0.2	)	(0.2	)
State income taxes, net of Federal income tax benefit	1.9		0.1		1.2
Uncertain tax positions	0.1		0.7		0.5
Amortization of net unfunded deferred taxes	0.7		0.9		0.6
Other	0.1		0.3		0.1
Effective income tax rate	30.5	%	26.4	%	30.4	%

(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, 2016and2015, respectively, were as follows:

December 31 (In millions)	2016			2015
Non-Current Deferred Income Tax Liabilities, net
Accelerated depreciation and other property related differences	$	2,103.2		$	2,016.0
Investment in Enable Midstream Partners	657.3			623.4
Regulatory asset	34.4			32.7
Income taxes refundable to customers, net	24.1			22.0
Company Pension Plan	16.5			13.7
Bond redemption-unamortized costs	4.3			4.8
Derivative instruments	2.2			1.5
Federal tax credits	(220.6		)	(184.4		)
State tax credits	(112.2		)	(106.7		)
Postretirement medical and life insurance benefits	(48.9		)	(56.2		)
Regulatory liabilities	(34.6		)	(46.3		)
Net operating losses	(31.7		)	(94.6		)
Asset retirement obligations	(24.5		)	(22.5		)
Accrued liabilities	(16.1		)	(14.0		)
Other	(14.0		)	(6.6		)
Accrued vacation	(3.5		)	(3.2		)
Deferred Federal investment tax credits	(0.8		)	(0.9		)
Uncollectible accounts	(0.6		)	(0.5		)
Non-Current Deferred Income Tax Liabilities, net	$	2,334.5		$	2,178.2

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, 2016, 2015, and 2014.

(In millions)	2016		2015		2014
Balance at January 1	$	20.2	$	16.1	$	12.0
Tax positions related to current year:
Additions	0.5		4.1		4.1
Balance at December 31	$	20.7	$	20.2	$	16.1

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	$	554.7	$	20.4	2030
Federal operating loss	32.2		11.3		2030
Federal tax credits	220.6		220.6		2029
State tax credits
Oklahoma investment tax credits	135.7		88.2		N/A
Oklahoma capital investment board credits	7.3		7.3		N/A
Oklahoma zero emission tax credits	24.1		16.2		2020
Louisiana inventory credits	0.7		0.5		2019