Retirement Plans and Postretirement Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan, Plan Assets, Contributions by Employer				$ 40.0
Pension Plan [Member]
Other Comprehensive Income (Loss), Defined Benefit Plan, Adjustment for Settlement or Curtailment Gain (Loss), Tax		$ 0.3	$ 0.5	1.9	$ 0.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		2.8	3.3	8.4	9.8
Interest cost		3.1	4.2	10.0	13.4
Expected return on plan assets		(8.5)	(9.4)	(25.6)	(28.0)
Amortization of net loss		2.3	4.3	7.0	12.7
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0.0	0.0	0.0	0.0
Settlement cost		3.7	12.1	35.4	12.1
Total net periodic benefit cost		3.4	14.5	35.2	20.0
Amount Attributable to Unconsolidated Affiliates	[1]	(0.1)	0.5	(0.2)	1.6
Net periodic benefit cost		3.5	14.0	35.4	18.4
Capitalized portion of net periodic pension benefit cost		0.9	0.9	2.5	2.7
Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.3	0.2	0.6	0.6
Interest cost		0.0	0.1	0.1	0.2
Expected return on plan assets		0.0	0.0	0.0	0.0
Amortization of net loss		0.0	0.1	0.1	0.4
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0.1	0.0	0.1	0.0
Settlement cost		1.7	0.4	2.1	0.7
Total net periodic benefit cost		2.1	0.8	3.0	1.9
Amount Attributable to Unconsolidated Affiliates	[1]	0.0	0.1	0.0	0.1
Net periodic benefit cost		2.1	0.7	3.0	1.8
Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.1	0.1	0.2	0.2
Interest cost		0.9	1.0	2.6	3.1
Expected return on plan assets		(0.4)	(0.5)	(1.4)	(1.4)
Amortization of net loss		0.7	0.5	2.1	1.5
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	[2]	(1.8)	(2.1)	(5.2)	(6.3)
Total net periodic benefit cost		(0.5)	(1.0)	(1.7)	(2.9)
Amount Attributable to Unconsolidated Affiliates	[1]	(0.1)	(0.2)	(0.4)	(0.6)
Net periodic benefit cost		(0.4)	(0.8)	(1.3)	(2.3)
Capitalized portion of net periodic pension benefit cost		0.1	0.0	0.2	0.1
OKLAHOMA | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost	[3]	4.4	10.8	33.3	11.1
Additional Pension Expense to Meet State Requirements	[3]	3.9	2.4	11.1	5.7
OKLAHOMA | Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Additional Pension Expense to Meet State Requirements	[4]	0.1	0.4	0.3	1.2
ARKANSAS | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement cost	[3]	0.4	1.0	3.1	1.0
OG&E [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer				30.0
OG&E [Member] | Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		2.0	2.3	5.8	6.8
Interest cost		2.3	3.2	7.3	10.0
Expected return on plan assets		(6.2)	(7.0)	(18.5)	(20.9)
Amortization of net loss		1.7	3.0	5.2	9.0
Settlement cost		2.6	10.3	29.2	10.3
Total net periodic benefit cost		2.4	11.8	29.0	15.2
Amount attributable to parent	[1]	0.7	1.5	5.3	2.5
Net periodic benefit cost		3.1	13.3	34.3	17.7
Capitalized portion of net periodic pension benefit cost		0.7	0.8	2.1	2.3
OG&E [Member] | Other Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.0	0.0	0.0	0.1
Interest cost		0.0	0.0	0.0	0.1
Expected return on plan assets		0.0	0.0	0.0	0.0
Amortization of net loss		0.0	0.1	0.1	0.3
Settlement cost		1.3	0.5	1.6	0.5
Total net periodic benefit cost		1.3	0.6	1.7	1.0
Amount attributable to parent	[1]	0.8	0.2	1.3	0.8
Net periodic benefit cost		2.1	0.8	3.0	1.8
OG&E [Member] | Postretirement Benefit Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost		0.0	0.0	0.1	0.1
Interest cost		0.6	0.8	1.9	2.4
Expected return on plan assets		(0.4)	(0.4)	(1.3)	(1.2)
Amortization of net loss		0.6	0.5	2.0	1.6
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	[2]	(1.2)	(1.5)	(3.7)	(4.6)
Total net periodic benefit cost		(0.4)	(0.6)	(1.0)	(1.7)
Amount attributable to parent	[1]	(0.1)	(0.2)	(0.3)	(0.6)
Net periodic benefit cost		(0.5)	(0.8)	(1.3)	(2.3)
Capitalized portion of net periodic pension benefit cost		$ 0.0	$ 0.0	$ 0.1	$ 0.1

[1] "Amount paid by unconsolidated affiliates" is only applicable to OGE Energy. "Amount allocated from OGE Energy" is only applicable to OG&E.

[2] 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.

[3] Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.

[4] Included in the Pension tracker, as presented in the regulatory assets and liabilities table in Note 1.