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Retirement Plans and Postretirement Benefit Plans - Schedule of Defined Benefit Plans Disclosures (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 5.3 $ 5.4 $ 7.6
Interest cost $ 15.6 $ 15.9 $ 15.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets $ (16.5) $ (16.2) $ (25.4)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net loss (gain) $ 6.5 $ 8.0 $ 8.9
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of unrecognized prior service cost [1] $ 0.0 $ 0.0 $ 0.0
Settlement cost 0.0 21.8 30.6
Net periodic benefit cost (income) 10.9 34.9 37.4
Pension Plan [Member] | Oklahoma Jurisdiction      
Defined Benefit Plan Disclosure [Line Items]      
Settlement cost [2] 0.0 20.1 15.4
Change in pension expense to maintain allowed recoverable amount in Oklahoma jurisdiction [2] 5.8 33.3 15.2
Pension Plan [Member] | Arkansas Jurisdiction      
Defined Benefit Plan Disclosure [Line Items]      
Settlement cost 0.0 [2] 1.9 [2] 1.4
Pension Plan [Member] | Og and E [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 5.3 4.4 6.2
Interest cost $ 13.4 $ 12.6 $ 12.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets $ (14.0) $ (12.9) $ (19.6)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net loss (gain) $ 6.2 $ 6.9 $ 7.4
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Settlement cost $ 0.0 $ 20.4 $ 12.9
Total net periodic benefit cost (income) 10.9 31.4 19.0
Amount Attributable to Parent 0.0 3.0 5.2
Net periodic benefit cost (income) 10.9 34.4 24.2
Other Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1.0 1.0 1.1
Interest cost $ 0.3 $ 0.3 $ 0.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets $ 0.0 $ 0.0 $ 0.0
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net loss (gain) $ 0.0 $ 0.0 $ 0.2
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of unrecognized prior service cost [1] $ 0.3 $ 0.3 $ 0.2
Settlement cost 0.0 0.5 0.3
Net periodic benefit cost (income) 1.6 2.1 2.0
Other Pension Plan [Member] | Og and E [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 0.1 0.0 0.0
Interest cost $ 0.1 $ 0.0 $ 0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets $ 0.0 $ 0.0 $ 0.0
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net loss (gain) $ 0.0 $ 0.0 $ 0.0
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Settlement cost $ 0.0 $ 0.4 $ 0.0
Total net periodic benefit cost (income) 0.2 0.4 0.0
Amount Attributable to Parent 1.4 1.7 1.5
Net periodic benefit cost (income) 1.6 2.1 1.5
Other Postretirement Benefits Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 0.1 0.1 0.2
Interest cost $ 5.2 $ 5.2 $ 3.5
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets $ (1.6) $ (1.7) $ (1.8)
Amortization of net loss (gain) $ (0.2) $ (0.2) $ 1.5
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of unrecognized prior service cost [3] $ 0.0 $ 0.0 $ (3.8)
Total net periodic benefit cost (income) 3.5 3.4 (0.4)
Net periodic benefit cost (income) 3.5 3.4 (0.4)
Other Postretirement Benefits Plan [Member] | Oklahoma Jurisdiction      
Defined Benefit Plan Disclosure [Line Items]      
Change in pension expense to maintain allowed recoverable amount in Oklahoma jurisdiction [4] 2.3 4.4 0.6
Other Postretirement Benefits Plan [Member] | Og and E [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 0.1 0.1 0.1
Interest cost $ 3.9 $ 3.9 $ 2.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets $ (1.4) $ (1.6) $ (1.6)
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net loss (gain) $ 0.0 $ 0.0 $ 1.5
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of unrecognized prior service cost [3] $ 0.0 $ 0.0 $ (3.6)
Total net periodic benefit cost (income) 2.6 2.4 (0.9)
Amount Attributable to Parent 0.5 0.5 0.0
Net periodic benefit cost (income) $ 3.1 $ 2.9 $ (0.9)
[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] Included in the pension regulatory asset in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.
[3] 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.
[4] Included in the pension regulatory asset, as indicated in the regulatory assets and liabilities table in Note 1.