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Retirement Plans and Postretirement Benefit Plans (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2023
Sep. 30, 2022
Pension Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost $ 1.3 $ 1.8 $ 4.0 $ 5.7
Interest cost 4.1 4.1 12.0 11.8
Expected return on plan assets (4.0) (6.0) (12.2) (19.0)
Amortization of net (gain) loss 1.8 2.4 6.0 6.6
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) 0.0 [1] 0.0 [1] 0.0 [1] 0.0 [2]
Settlement cost 1.7 2.3 21.1 18.3
Total net periodic benefit cost 4.9 4.6 30.9 23.4
Capitalized portion of net periodic pension benefit cost 0.6 0.7 1.7 2.2
Other Pension Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost 0.2 0.3 0.7 0.8
Interest cost 0.1 0.0 0.2 0.1
Expected return on plan assets 0.0 0.0 0.0 0.0
Amortization of net (gain) loss 0.0 0.0 0.0 0.1
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) [1] 0.1 0.1 0.3 0.2
Settlement cost 0.1 0.0 0.1 0.2
Total net periodic benefit cost 0.5 0.4 1.3 1.4
Postretirement Benefit Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost 0.1 0.0 0.1 0.1
Interest cost 1.3 0.9 3.9 2.7
Expected return on plan assets (0.5) (0.5) (1.3) (1.4)
Amortization of net (gain) loss (0.1) 0.5 (0.2) 1.2
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) 0.0 [2] (1.0) [2] 0.0 [1] (2.9) [1]
Total net periodic benefit cost 0.8 (0.1) 2.5 (0.3)
Net periodic benefit cost (income) 0.8 (0.1) 2.5 (0.3)
Capitalized portion of net periodic pension benefit cost 0.0 0.1 0.1 0.2
OG&E [Member] | Pension Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost 1.1 1.5 3.3 4.6
Interest cost 3.1 3.1 9.4 9.0
Expected return on plan assets (3.1) (4.7) (9.6) (14.7)
Amortization of net (gain) loss 1.6 2.1 5.2 5.6
Settlement cost 1.7 0.4 19.7 6.1
Total net periodic benefit cost 4.4 2.4 28.0 10.6
Net periodic benefit cost (income) 4.9 2.8 30.5 13.2
Capitalized portion of net periodic pension benefit cost 0.4 0.7 1.4 1.9
Amount Attributable to Parent 0.5 0.4 2.5 2.6
OG&E [Member] | Other Pension Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost 0.0 0.0 0.0 0.0
Interest cost 0.0 0.0 0.0 0.0
Expected return on plan assets 0.0 0.0 0.0 0.0
Amortization of net (gain) loss 0.0 0.0 0.0 0.0
Settlement cost 0.1 0.0 0.1 0.0
Total net periodic benefit cost 0.1 0.0 0.1 0.0
Net periodic benefit cost (income) 0.5 0.4 1.2 1.1
Amount Attributable to Parent 0.4 0.4 1.1 1.1
OG&E [Member] | Postretirement Benefit Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Service cost 0.0 0.0 0.0 0.1
Interest cost 0.9 0.7 2.9 2.0
Expected return on plan assets (0.3) (0.4) (1.1) (1.2)
Amortization of net (gain) loss 0.0 0.3 0.0 1.1
Defined Benefit Plan, Amortization of Prior Service Cost (Credit) [1] 0.0 (0.9) 0.0 (2.7)
Total net periodic benefit cost 0.6 (0.3) 1.8 (0.7)
Net periodic benefit cost (income) 0.7 (0.3) 2.2 (0.7)
Capitalized portion of net periodic pension benefit cost 0.0 0.0 0.1 0.1
Amount Attributable to Parent 0.1 0.0 0.4 0.0
OKLAHOMA | Pension Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Settlement cost 1.7 [3] 0.3 [3] 19.1 [4] 7.0 [4]
Change in regulatory asset related to pension expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) 5.0 [3] 2.7 [3] 29.0 [4] 5.0 [4]
OKLAHOMA | Postretirement Benefit Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Change in regulatory asset related to pension expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) [4] 1.1 (0.2) 3.3 (0.4)
ARKANSAS | Pension Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Settlement cost $ 0.2 [3] $ 0.1 [3] $ 1.8 [4] $ 0.7 [4]
[1] 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.
[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 in each jurisdiction, as presented in the regulatory assets and liabilities table in Note 1.
[4] Included in the pension regulatory asset or liability in each jurisdiction, as presented in the regulatory assets and liabilities table in Note 1.