Retirement Plans and Postretirement Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2019

Defined Benefit Plan [Abstract]

Schedule of Defined Benefit Plans Disclosures [Table Text Block]

The following table presents the net periodic benefit cost components, before consideration of capitalized amounts, of the Company's Pension Plan, Restoration of Retirement Income Plan and postretirement benefit plans that are included in the Condensed Consolidated Financial Statements. Service cost is presented within Other Operation and Maintenance, and interest cost, expected return on plan assets, amortization of net loss, amortization of unrecognized prior service cost and settlement cost are presented within Other Net Periodic Benefit Expense in the Company's Condensed Consolidated Statements of Income. OG&E recovers specific amounts of pension and postretirement medical costs in rates approved in its Oklahoma rate reviews. In accordance with approved orders, OG&E defers the difference between actual pension and postretirement medical expenses and the amount approved in its last Oklahoma rate review as a regulatory asset or regulatory liability. These amounts have been recorded in the Pension tracker in the regulatory assets and liabilities table in Note 1 and within Other Net Periodic Benefit Expense in the Company's Condensed Consolidated Statements of Income.

	Pension Plan												Restoration of Retirement Income Plan
	Three Months Ended						Nine Months Ended						Three Months Ended				Nine Months Ended
	September 30,						September 30,						September 30,				September 30,
(In millions)	2019			2018			2019			2018			2019		2018		2019		2018
Service cost	$	3.4		$	3.6		$	9.7		$	11.1		$	0.1	$	0.1	$	0.3	$	0.3
Interest cost	4.6			6.1			15.5			17.8			0.1		0.1		0.3		0.3
Expected return on plan assets	(9.5		)	(10.7		)	(27.1		)	(33.0		)	—		—		—		—
Amortization of net loss	4.4			3.9			13.0			12.2			0.1		0.1		0.3		0.5
Amortization of unrecognized prior service cost (A)	—			—			—			—			—		0.1		—		0.1
Settlement cost	2.8			12.2			23.4			12.2			0.4		0.6		0.4		0.6
Total net periodic benefit cost	5.7			15.1			34.5			20.3			0.7		1.0		1.3		1.8
Less: Amount paid by unconsolidated affiliates	0.5			0.7			2.2			1.9			0.1		0.1		0.1		0.1
Net periodic benefit cost	$	5.2		$	14.4		$	32.3		$	18.4		$	0.6	$	0.9	$	1.2	$	1.7

(A) Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment.

In addition to the net periodic benefit cost amounts presented in the above table for the three and nine months ended September 30, 2019 and 2018, the Company also recognized the following:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(In millions)	2019		2018		2019			2018
Increase (decrease) of pension expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A)	$	1.5	$	—	$	(0.2	)	$	7.8
Deferral of pension expense related to pension settlement charges:
Oklahoma jurisdiction (A)	$	2.3	$	10.5	$	14.0		$	10.5
Arkansas jurisdiction (A)	$	0.2	$	1.0	$	1.3		$	1.0

(A) Included in the Pension tracker regulatory liability for the Oklahoma jurisdiction and in the deferred pension expenses regulatory asset for the Arkansas jurisdiction (see Note 1).

	Postretirement Benefit Plans
	Three Months Ended						Nine Months Ended
	September 30,						September 30,
(In millions)	2019			2018			2019			2018
Service cost	$	0.1		$	—		$	0.2		$	0.2
Interest cost	1.2			1.5			4.2			4.1
Expected return on plan assets	(0.5		)	(0.5		)	(1.4		)	(1.5		)
Amortization of net loss	0.5			1.0			1.5			2.9
Amortization of unrecognized prior service cost (A)	(2.1		)	(2.1		)	(6.3		)	(6.3		)
Total net periodic benefit cost	(0.8		)	(0.1		)	(1.8		)	(0.6		)
Less: Amount paid by unconsolidated affiliates	(0.2		)	(0.2		)	(0.5		)	(0.4		)
Net periodic benefit cost	$	(0.6	)	$	0.1		$	(1.3	)	$	(0.2	)

(A) Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment.

In addition to the net periodic benefit income and cost amounts presented in the above table for the three and nine months ended September 30, 2019 and 2018, the Company also recognized the following:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(In millions)	2019		2018		2019		2018
Increase of postretirement expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A)	$	0.1	$	0.1	$	0.9	$	4.3

(A) Included in the Pension tracker regulatory liability (see Note 1).

Schedule of Capitalized Pension and Postretirement Cost [Table Text Block]

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(In millions)	2019		2018		2019		2018
Capitalized portion of net periodic pension benefit cost	$	0.9	$	0.9	$	2.7	$	2.8
Capitalized portion of net periodic postretirement benefit cost	$	—	$	—	$	0.1	$	0.1