Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Taxes [Abstract]

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

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

Year Ended December 31 (In millions)	2019		2018		2017
Provision (benefit) for current income taxes:
Federal	$	(6.4)	$	(1.9)	$	4.9
State	5.1		(4.4)		(4.2)
Total provision (benefit) for current income taxes	(1.3)		(6.3)		0.7
Provision (benefit) for deferred income taxes, net:
Federal	48.5		74.7		(75.9)
State	(17.4)		3.7		26.0
Total provision (benefit) for deferred income taxes, net	31.1		78.4		(49.9)
Deferred federal investment tax credits, net	—		0.1		(0.1)
Total income tax expense (benefit)	$	29.8	$	72.2	$	(49.3)

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	2019		2018		2017
Statutory federal tax rate	21.0	%	21.0	%	35.0	%
Executive compensation limitation	0.2		0.2		—
Federal renewable energy credit (A)	(6.0)		(5.1)		(4.8)
Amortization of net unfunded deferred taxes	(4.5)		(2.1)		0.7
State income taxes, net of federal income tax benefit	(1.2)		0.4		2.0
Stock-based compensation	(1.2)		—		—
Remeasurement of state deferred tax liabilities	(0.8)		(0.4)		0.4
Other	(0.7)		0.4		(0.1)
401(k) dividends	(0.4)		(0.3)		(0.5)
Federal deferred tax revaluation	—		0.4		(41.2)
Federal investment tax credits, net	—		—		(0.1)
Effective income tax rate	6.4	%	14.5	%	(8.6)	%

(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 at December 31, 2019 and 2018 were as follows:

December 31 (In millions)	2019		2018
Deferred income tax liabilities, net:
Accelerated depreciation and other property related differences	$	1,656.8	$	1,605.3
Investment in Enable	478.2		469.9
Regulatory assets	28.4		17.4
Company Pension Plan	4.1		7.6
Bond redemption-unamortized costs	2.2		2.4
Derivative instruments	1.6		1.7
Other	0.4		1.1
Federal tax credits	(238.0)		(237.8)
Income taxes recoverable from customers, net	(229.9)		(239.6)
State tax credits	(185.8)		(156.0)
Regulatory liabilities	(68.1)		(78.8)
Postretirement medical and life insurance benefits	(23.3)		(23.6)
Asset retirement obligations	(19.2)		(21.5)
Net operating losses	(16.6)		(20.2)
Accrued liabilities	(10.7)		(12.5)
Accrued vacation	(2.1)		(2.3)
Deferred federal investment tax credits	(1.8)		(1.8)
Uncollectible accounts	(0.4)		(0.4)
Total deferred income tax liabilities, net	$	1,375.8	$	1,310.9

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, 2019, 2018 and 2017.

(In millions)	2019		2018		2017
Balance at January 1	$	20.7	$	20.7	$	20.7
Tax positions related to current year:
Additions	—		—		—
Balance at December 31	$	20.7	$	20.7	$	20.7

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	$	371.6	$	16.6	2030
Federal tax credits	$	238.0	$	238.0	2032
State tax credits:
Oklahoma investment tax credits	$	183.9	$	145.3	N/A
Oklahoma capital investment board credits	$	12.4	$	12.4	N/A
Oklahoma zero emission tax credits	$	34.9	$	28.0	2020
Louisiana inventory credits	$	0.2	$	0.1	2020

N/A - not applicable