Retirement Plans and Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended				12 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2013
Defined Benefit Plan, Plan Assets, Contributions by Employer						$ 15.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost						(8.6)
Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		$ 0.0	[1]	$ 0.1	[1]	0.1	[2]	$ 0.1	[2]
Interest cost		0.1	[1]	0.0	[1]	0.2	[2]	0.1	[2]
Expected return on plan assets		0.0	[1]	0.0	[1]	0.0	[2]	0.0	[2]
Amortization of net loss		0.1	[1]	0.1	[1]	0.4	[2]	0.3	[2]
Settlement cost		0.0	[1]	0.0	[1]	0.0	[2]	0.0	[2]
Net periodic benefit cost		0.2	[1]	0.2	[1]	0.7	[2]	0.5	[2]
Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		2.4	[1]	2.5	[1]	7.4	[2]	7.6	[2]
Interest cost		4.5	[1]	4.9	[1]	13.2	[2]	14.6	[2]
Expected return on plan assets		(8.0)	[1]	(8.2)	[1]	(24.9)	[2]	(24.6)	[2]
Amortization of net loss		3.0	[1]	3.2	[1]	9.1	[2]	9.7	[2]
Settlement cost		8.6	[1]	0.0	[1]	8.6	[2]	0.0	[2]	$ (22.4)
Net periodic benefit cost		10.5	[1]	2.4	[1]	13.4	[2]	7.3	[2]
Capitalized Portion of Net Periodic Benefit Cost		0.8		0.8		2.4		2.6
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.1	[3]	0.1	[3]	0.2	[4]	0.3	[4]
Interest cost		1.0	[3]	1.2	[3]	3.1	[4]	4.5	[4]
Expected return on plan assets		(0.5)	[3]	(0.5)	[3]	(1.4)	[4]	(1.5)	[4]
Amortization of net loss		1.0	[3]	0.5	[3]	2.9	[4]	1.3	[4]
Amortization of unrecognized prior service cost	[5]	(1.5)	[3]	(1.0)	[3]	(4.6)	[4]	(1.0)	[4]
Settlement cost		0.0	[3]	0.4	[3]	0.0	[4]	0.4	[4]
Net periodic benefit cost		0.1	[3]	0.7	[3]	0.2	[4]	4.0	[4]
Capitalized Portion of Net Periodic Benefit Cost		0.0		0.1		0.1		1.2
OKLAHOMA
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Additional Pension Expense to Meet State Requirements				2.7		7.8		8.5
OKLAHOMA | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost		(7.8)				(7.8)
OKLAHOMA | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Additional Pension Expense to Meet State Requirements		0.1		1.9		4.3		3.9
ARKANSAS | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost		(0.7)				(0.7)		(2.3)
OGE Energy [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost		0.7	[1]	0.0	[1]	1.0	[2]	0.0	[2]
OGE Energy [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost		2.7	[1]	0.0	[1]	3.7	[2]	0.0	[2]
OGE Energy [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost		(0.2)	[3]	0.0	[3]	(0.5)	[4]	0.0	[4]
Og and E [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer						5.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	[1]	14.1		2.6		18.8		7.8
Og and E [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost		0.9	[1]	0.2	[1]	1.7	[2]	0.5	[2]
Og and E [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost		13.2	[1]	2.4	[1]	17.1	[2]	7.3	[2]
Og and E [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost		$ (0.1)	[3]	$ 0.7	[3]	$ (0.3)	[4]	$ 4.0	[4]

[1] In addition to the $14.1 million and $2.6 million of net periodic benefit cost recognized during the three months ended September 30, 2018 and 2017, respectively, OG&E recognized the following:•a deferral of pension expense during the three months ended September 30, 2018 of $7.8 million, which includes a portion of OGE Energy's pension settlement charge, related to the pension settlement charge of $8.6 million in accordance with the Oklahoma Pension tracker regulatory liability (see Note 1);•a deferral of pension expense during the

[2] In addition to the $18.8 million and $7.8 million of net periodic benefit cost recognized during the nine months ended September 30, 2018 and 2017, respectively, OG&E recognized the following:•an increase in pension expense during the nine months ended September 30, 2018 and 2017 of $7.8 million and $8.5 million, respectively, to maintain the allowable amount to be recovered for pension expense in the Oklahoma jurisdiction, which are included in the Pension tracker regulatory liability (see Note 1);•a deferral of pension expense during the nine months ended September 30, 2018 of $7.8 million, which includes a portion of OGE Energy's pension settlement charge, related to the pension settlement charge of $8.6 million in accordance with the Oklahoma Pension tracker regulatory liability (see Note 1); •a deferral of pension expense during the nine months ended September 30, 2018 of $0.7 million related to the Arkansas jurisdictional portion of the pension settlement charge of $8.6 million; and•a deferral of pension expense during the nine months ended September 30, 2017 of $2.3 million related to the Arkansas jurisdictional portion of the pension settlement charge of $22.4 million in 2013.

[3] In addition to the $0.1 million of net periodic benefit income and $0.7 million of net periodic benefit cost recognized during the three months ended September 30, 2018 and 2017, respectively, OG&E recognized an increase in postretirement medical expense in the three months ended September 30, 2018 and 2017 of $0.1 million and $1.9 million, respectively, to maintain the allowable amount to be recovered for postretirement medical expense in the Oklahoma jurisdiction which are included in the Pension tracker regulatory liability (see Note 1).

[4] In addition to the $0.3 million of net periodic benefit income and $4.0 million of net periodic benefit cost recognized during the nine months ended September 30, 2018 and 2017, respectively, OG&E recognized an increase in postretirement medical expense in the nine months ended September 30, 2018 and 2017 of $4.3 million and $3.9 million, respectively, to maintain the allowable amount to be recovered for postretirement medical expense in the Oklahoma jurisdiction which are included in the Pension tracker regulatory liability (see Note 1).

[5] 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.