Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [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)	2018			2017			2016
Provision (benefit) for current income taxes:
Federal	$	(12.4	)	$	26.3		$	2.9
State	(4.1		)	(4.3		)	(5.3		)
Total provision (benefit) for current income taxes	(16.5		)	22.0			(2.4		)
Provision for deferred income taxes, net:
Federal	53.7			100.0			99.8
State	2.7			19.9			17.2
Total provision for deferred income taxes, net	56.4			119.9			117.0
Deferred federal investment tax credits, net	0.1			(0.1		)	(0.2		)
Total income tax expense	$	40.0		$	141.8		$	114.4

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	2018		2017		2016
Statutory federal tax rate	21.0	%	35.0	%	35.0	%
Federal renewable energy credit (A)	(6.9	)	(6.1	)	(8.2	)
Amortization of net unfunded deferred taxes	(2.9	)	0.9		0.8
State income taxes, net of federal income tax benefit	(0.2	)	2.2		1.8
Other	(0.1	)	(0.3	)	0.1
Uncertain tax positions	—		—		0.1
Federal investment tax credits, net	—		—		(0.9	)
Effective income tax rate	10.9	%	31.7	%	28.7	%

(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, 2018and2017were as follows:

December 31 (In millions)	2018			2017
Deferred income tax liabilities, net:
Accelerated depreciation and other property related differences	$	1,605.3		$	1,449.6
OG&E Pension Plan	26.0			28.4
Regulatory assets	17.4			18.9
Bond redemption-unamortized costs	2.4			2.6
Income taxes recoverable from customers, net	(239.6		)	(244.3		)
Federal tax credits	(237.5		)	(218.3		)
State tax credits	(142.3		)	(129.2		)
Regulatory liabilities	(78.8		)	(16.8		)
Asset retirement obligations	(21.5		)	(19.2		)
Postretirement medical and life insurance benefits	(16.2		)	(17.4		)
Net operating losses	(10.0		)	(11.2		)
Accrued liabilities	(6.1		)	(3.8		)
Other	(2.4		)	(4.8		)
Deferred federal investment tax credits	(1.9		)	(0.5		)
Accrued vacation	(1.7		)	(1.4		)
Uncollectible accounts	(0.4		)	(0.4		)
Total deferred income tax liabilities, net	$	892.7		$	832.2

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, 2018, 2017 and 2016.

(In millions)	2018		2017		2016
Balance at January 1	$	20.7	$	20.7	$	20.2
Tax positions related to current year:
Additions	—		—		0.5
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	$	223.7	$	10.0	2030
Federal tax credits	$	237.5	$	237.5	2032
State tax credits:
Oklahoma investment tax credits	$	144.3	$	114.0	N/A
Oklahoma capital investment board credits	$	8.9	$	8.9	N/A
Oklahoma zero emission tax credits	$	24.1	$	19.4	2020

N/A - not applicable