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Retirement Plans and Postretirement Benefit Plans (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 6 Months Ended
Mar. 31, 2026
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Employer contribution paid $ 5.0        
Pension Plan [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost   $ 1.2 $ 1.3 $ 2.6 $ 2.7
Interest cost   $ 4.0 $ 4.1 $ 7.9 $ 8.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets   $ (4.6) $ (4.2) $ (8.7) $ (8.3)
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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net (gain) loss   $ 1.4 $ 1.6 $ 3.0 $ 3.1
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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of unrecognized prior service cost [1]   $ 0.0 $ 0.0 $ 0.0 $ 0.0
Net periodic benefit cost   2.0 2.8 4.8 5.6
Capitalized portion of net periodic pension benefit cost   0.6 0.6 1.2 1.2
Other Pension Plan [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost   0.3 0.2 0.6 0.5
Interest cost   $ 0.2 $ 0.1 $ 0.3 $ 0.2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets   $ 0.0 $ 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net (gain) loss   $ 0.0 $ 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of unrecognized prior service cost [1]   $ 0.0 $ 0.2 $ 0.1 $ 0.2
Net periodic benefit cost   0.5 0.5 1.0 0.9
Postretirement Benefit Plan [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost   0.0 0.0 0.0 0.0
Interest cost   1.0 1.4 2.2 2.7
Expected return on plan assets   (0.3) (0.4) (0.7) (0.8)
Amortization of net (gain) loss   (0.1) 0.2 (0.1) 0.2
Total net periodic benefit cost   0.6 1.2 1.4 2.1
Net periodic benefit cost   0.6 1.2 1.4 2.1
Capitalized portion of net periodic pension benefit cost   0.0 0.0 0.0 0.0
OG&E [Member] | Pension Plan [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost   1.2 1.3 2.6 2.7
Interest cost   $ 3.4 $ 3.6 $ 6.8 $ 7.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets   $ (3.9) $ (3.6) $ (7.5) $ (7.1)
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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net (gain) loss   $ 1.3 $ 1.5 $ 2.8 $ 2.9
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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Total net periodic benefit cost   $ 2.0 $ 2.8 $ 4.7 $ 5.6
Plus: Amount allocated from OGE Energy   0.0 0.0 0.0 0.0
Net periodic benefit cost   2.0 2.8 4.7 5.6
Capitalized portion of net periodic pension benefit cost   0.6 0.6 1.2 1.2
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   $ 0.1 $ 0.1 $ 0.1 $ 0.1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Expected return on plan assets   $ 0.0 $ 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Amortization of net (gain) loss   $ 0.0 $ 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) Pension and Other Postretirement Benefits Cost (Reversal of Cost)
Total net periodic benefit cost   $ 0.1 $ 0.1 $ 0.1 $ 0.1
Plus: Amount allocated from OGE Energy   0.5 0.4 0.9 0.8
Net periodic benefit cost   0.6 0.5 1.0 0.9
OG&E [Member] | Postretirement Benefit Plan [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Service cost   0.0 0.0 0.0 0.0
Interest cost   0.8 1.1 1.7 2.1
Expected return on plan assets   (0.3) (0.3) (0.6) (0.7)
Amortization of net (gain) loss   0.0 0.2 0.0 0.3
Total net periodic benefit cost   0.5 1.0 1.1 1.7
Plus: Amount allocated from OGE Energy   0.1 0.1 0.2 0.2
Net periodic benefit cost   0.6 1.1 1.3 1.9
Capitalized portion of net periodic pension benefit cost   0.0 0.0 0.0 0.0
Oklahoma Jurisdiction | Pension Plan [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Change in pension/postretirement expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) [2]   (0.8) (0.2) (1.1) (0.4)
OKLAHOMA | Postretirement Benefit Plan [Member]          
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]          
Change in pension/postretirement expense to maintain allowed recoverable amount in Oklahoma jurisdiction (A) [3]   $ (0.2) $ 0.3 $ (0.2) $ 0.3
[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, as indicated in the regulatory assets and liabilities table in Note 1.
[3] Included in the pension regulatory asset, as indicated in the regulatory assets and liabilities table in Note 1.