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v3.20.4

Retirement Plans and Postretirement Benefit Plans (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match |  |  | 200.00% |  |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay |  |  | 5.00% |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Employer contributions |  | $ 40.0 | $ 20.0 |  | $ 20.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Ultimate Health Care Cost Trend Rate |  |  | 4.50% |  |  |  |
Expected Future Benefit Payments, Next Twelve Months |  |  | $ 164.2 |  |  |  |
Expected Future Benefit Payments, Year Two |  |  | 43.3 |  |  |  |
Expected Future Benefit Payments, Year Three |  |  | 42.5 |  |  |  |
Expected Future Benefit Payments, Year Four |  |  | 44.2 |  |  |  |
Expected Future Benefit Payments, Year Five |  |  | 41.1 |  |  |  |
Expected Future Benefit Payments, Five Fiscal Years Thereafter |  |  | 203.6 |  |  |  |
Defined Contribution Plan, Cost |  |  | 18.2 |  | 14.4 |  | $ 13.2
Postemployment Benefits Liability |  |  | 2.2 |  | 2.1 |  |
Og and E [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Employer contributions |  |  | 10.0 |  | 5.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Expected Future Benefit Payments, Next Twelve Months |  |  | 123.9 |  |  |  |
Expected Future Benefit Payments, Year Two |  |  | 33.1 |  |  |  |
Expected Future Benefit Payments, Year Three |  |  | 31.9 |  |  |  |
Expected Future Benefit Payments, Year Four |  |  | 32.3 |  |  |  |
Expected Future Benefit Payments, Year Five |  |  | 29.3 |  |  |  |
Expected Future Benefit Payments, Five Fiscal Years Thereafter |  |  | 141.1 |  |  |  |
Defined Contribution Plan, Cost |  |  | 14.3 |  | 11.0 |  | 9.8
Postemployment Benefits Liability |  |  | 1.8 |  | 1.7 |  |
Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Benefits Paid |  |  | (14.2) |  | (14.6) |  |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  | 654.6 | 616.1 |  | 615.9 |  |
Service cost |  |  | 13.2 |  | 12.9 |  | 14.9
Interest cost |  |  | 17.0 |  | 20.7 |  | 23.8
Plan curtailments |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits |  |  | 7.6 |  | 0.0 |  |
Plan settlements |  |  | (42.8) |  | (83.1) |  |
Actuarial losses |  |  | 57.7 |  | 64.3 |  |
Benefit Obligation, Ending |  |  | 654.6 |  | 616.1 |  | 615.9
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 570.3 | 530.3 |  | 522.8 |  |
Actual return on plans' assets |  |  | 77.0 |  | 85.2 |  |
Employer contributions |  |  | 20.0 |  | 20.0 |  |
Plan settlements |  |  | (42.8) |  | (83.1) |  |
Fair Value of Plan Assets, Ending |  |  | 570.3 |  | 530.3 |  | 522.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  | 13.2 |  | 12.9 |  | 14.9
Interest cost |  |  | 17.0 |  | 20.7 |  | 23.8
Expected return on plan assets |  |  | (37.6) |  | (36.1) |  | (44.1)
Defined Benefit Plan, Amortization of Gain (Loss) |  |  | (17.1) |  | (17.3) |  | (16.2)
Amortization of unrecognized prior service cost | [1] |  | 0.0 |  | 0.0 |  | 0.0
Curtailment |  |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits |  |  | 7.6 |  | 0.0 |  | 0.0
Settlement cost |  |  | 14.1 |  | 27.6 |  | 25.1
Net periodic benefit cost |  |  | 31.4 |  | 42.4 |  | 35.9
Amount paid by unconsolidated affiliates | [2] |  | 2.0 |  | 2.9 |  | 2.5
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  |  | 29.4 |  | 39.5 |  | 33.4
Plan settlements |  |  | (42.8) |  | (83.1) |  |
Capitalized Portion of Net Periodic Benefit Cost |  |  | $ 3.8 |  | $ 3.6 |  | $ 3.8
Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  | 2.30% |  | 3.15% |  | 4.20%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets |  |  | 7.50% |  | 7.50% |  | 7.50%
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  |  | 4.20% |  | 4.20% |  | 4.20%
Fair Value of Plan Assets, Beginning |  | 570.3 | $ 530.3 |  | $ 522.8 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  | (14.2) |  | (14.6) |  |
Accumulated Benefit Obligation |  |  | (610.8) |  | (563.3) |  |
Pension Plans, Defined Benefit [Member] | Og and E [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Benefits Paid |  |  | (12.3) |  | (12.7) |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  | 484.1 | 462.0 |  | 453.6 |  |
Service cost |  |  | 9.2 |  | 9.0 |  | $ 9.8
Interest cost |  |  | 12.6 |  | 15.6 |  | 17.6
Plan curtailments |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits |  |  | 5.1 |  | 0.0 |  |
Plan settlements |  |  | (33.5) |  | (45.6) |  |
Actuarial losses |  |  | 41.0 |  | 42.1 |  |
Benefit Obligation, Ending |  |  | 484.1 |  | 462.0 |  | 453.6
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 420.3 | 399.1 |  | 387.6 |  |
Actual return on plans' assets |  |  | 57.0 |  | 64.8 |  |
Employer contributions |  |  | 10.0 |  | 5.0 |  |
Plan settlements |  |  | (33.5) |  | (45.6) |  |
Fair Value of Plan Assets, Ending |  |  | 420.3 |  | 399.1 |  | 387.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  | 9.2 |  | 9.0 |  | 9.8
Interest cost |  |  | 12.6 |  | 15.6 |  | 17.6
Expected return on plan assets |  |  | (27.9) |  | (27.6) |  | (33.1)
Defined Benefit Plan, Amortization of Gain (Loss) |  |  | (12.1) |  | (12.9) |  | (12.1)
Amortization of unrecognized prior service cost |  |  | 0.0 |  | 0.0 |  | 0.0
Curtailment |  |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits |  |  | 5.1 |  | 0.0 |  | 0.0
Settlement cost |  |  | 11.4 |  | 16.4 |  | 19.4
Net periodic benefit cost |  |  | 22.5 |  | 26.3 |  | 25.8
Amount Attributable to Parent | [2] |  | 5.9 |  | 4.5 |  | 5.7
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  |  | 28.4 |  | 30.8 |  | 31.5
Plan settlements |  |  | (33.5) |  | (45.6) |  |
Capitalized Portion of Net Periodic Benefit Cost |  |  | 3.1 |  | 3.0 |  | 3.2
Fair Value of Plan Assets, Beginning |  | 420.3 | 399.1 |  | 387.6 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  | (12.3) |  | (12.7) |  |
Accumulated Benefit Obligation |  |  | (454.7) |  | (425.8) |  |
Pension Plans, Defined Benefit [Member] | OKLAHOMA |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Settlement cost | [3] |  | 21.6 |  | 17.9 |  | 22.1
Additional Pension Expense to Meet State Requirements |  |  | (13.8) | [3] | (16.1) |  | (14.1)
Pension Plans, Defined Benefit [Member] | ARKANSAS |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Settlement cost | [3] |  | 2.0 |  | 1.7 |  | 2.1
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Restoration of Retirement Income Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Benefits Paid |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment |  |  | 0.0 |  | 0.3 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  | 7.8 | 10.3 |  | 9.6 |  |
Service cost |  |  | 0.8 |  | 0.5 |  | 0.4
Interest cost |  |  | 0.2 |  | 0.4 |  | 0.3
Plan curtailments |  |  | 0.2 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits |  |  | 0.0 |  | 0.0 |  |
Plan settlements |  |  | (5.3) |  | (1.2) |  |
Actuarial losses |  |  | 1.6 |  | 0.7 |  |
Benefit Obligation, Ending |  |  | 7.8 |  | 10.3 |  | 9.6
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  | 0.0 |  |
Actual return on plans' assets |  |  | 0.0 |  | 0.0 |  |
Employer contributions |  |  | 5.3 |  | 1.2 |  |
Plan settlements |  |  | (5.3) |  | (1.2) |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  | 0.8 |  | 0.5 |  | 0.4
Interest cost |  |  | 0.2 |  | 0.4 |  | 0.3
Expected return on plan assets |  |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Amortization of Gain (Loss) |  |  | (0.5) |  | (0.5) |  | (0.7)
Amortization of unrecognized prior service cost | [1] |  | 0.0 |  | 0.0 |  | 0.1
Curtailment |  |  | 0.2 |  | 0.0 |  | 0.0
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits |  |  | 0.0 |  | 0.0 |  | 0.0
Settlement cost |  |  | 2.7 |  | 0.5 |  | 1.0
Net periodic benefit cost |  |  | 4.4 |  | 1.9 |  | 2.5
Amount paid by unconsolidated affiliates | [2] |  | 0.1 |  | 0.1 |  | 0.1
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  |  | 4.3 |  | 1.8 |  | 2.4
Plan settlements |  |  | (5.3) |  | (1.2) |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  | 0.0 |  | 0.0 |  |
Accumulated Benefit Obligation |  |  | (6.9) |  | (8.1) |  |
Restoration of Retirement Income Plan [Member] | Og and E [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Benefits Paid |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  | 3.0 | 6.1 |  | 6.0 |  |
Service cost |  |  | 0.1 |  | 0.2 |  | 0.2
Interest cost |  |  | 0.1 |  | 0.2 |  | 0.2
Plan curtailments |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits |  |  | 0.0 |  | 0.0 |  |
Plan settlements |  |  | (4.5) |  | (0.9) |  |
Actuarial losses |  |  | 1.2 |  | 0.6 |  |
Benefit Obligation, Ending |  |  | 3.0 |  | 6.1 |  | 6.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  | 0.0 |  |
Actual return on plans' assets |  |  | 0.0 |  | 0.0 |  |
Employer contributions |  |  | 4.5 |  | 0.9 |  |
Plan settlements |  |  | (4.5) |  | (0.9) |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  | 0.1 |  | 0.2 |  | 0.2
Interest cost |  |  | 0.1 |  | 0.2 |  | 0.2
Expected return on plan assets |  |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Amortization of Gain (Loss) |  |  | (0.4) |  | (0.3) |  | (0.5)
Amortization of unrecognized prior service cost |  |  | 0.0 |  | 0.0 |  | 0.0
Curtailment |  |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits |  |  | 0.0 |  | 0.0 |  | 0.0
Settlement cost |  |  | 2.4 |  | 0.5 |  | 0.4
Net periodic benefit cost |  |  | 3.0 |  | 1.2 |  | 1.3
Amount Attributable to Parent | [2] |  | 1.3 |  | 0.5 |  | 1.2
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  |  | 4.3 |  | 1.7 |  | 2.5
Plan settlements |  |  | (4.5) |  | (0.9) |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  | 0.0 |  | 0.0 |  |
Accumulated Benefit Obligation |  |  | (2.9) |  | (4.8) |  |
Other Postretirement Benefits Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Benefits Paid |  |  | (11.0) |  | (12.1) |  |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  | 144.5 | 136.5 |  | 135.8 |  |
Service cost |  |  | 0.2 |  | 0.2 |  | 0.3
Interest cost |  |  | 4.2 |  | 5.6 |  | 5.4
Plan curtailments |  |  | 4.0 |  | 0.0 |  |
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant |  |  | (3.3) |  | (4.1) |  |
Actuarial losses |  |  | 7.3 |  | 2.9 |  |
Benefit Obligation, Ending |  |  | 144.5 |  | 136.5 |  | 135.8
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 47.6 | 47.0 |  | 45.3 |  |
Actual return on plans' assets |  |  | 1.2 |  | 4.6 |  |
Employer contributions |  |  | 7.1 |  | 5.1 |  |
Fair Value of Plan Assets, Ending |  |  | 47.6 |  | 47.0 |  | 45.3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  | 0.2 |  | 0.2 |  | 0.3
Interest cost |  |  | 4.2 |  | 5.6 |  | 5.4
Expected return on plan assets |  |  | (1.8) |  | (1.9) |  | (2.0)
Defined Benefit Plan, Amortization of Gain (Loss) |  |  | (2.0) |  | (2.0) |  | (3.8)
Amortization of unrecognized prior service cost | [1] |  | (8.4) |  | (8.4) |  | (8.4)
Curtailment |  |  | (1.5) |  | 0.0 |  | 0.0
Net periodic benefit cost |  |  | (2.3) |  | (2.5) |  | (0.9)
Amount paid by unconsolidated affiliates | [4] |  | (0.7) |  | (0.6) |  | (0.5)
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  |  | (1.6) |  | (1.9) |  | (0.4)
Capitalized Portion of Net Periodic Benefit Cost |  |  | $ 0.2 |  | $ 0.2 |  | $ 0.2
Assumptions Used Calculating Benefit Obligation, Discount Rate |  |  | 2.45% |  | 3.25% |  | 4.30%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets |  |  | 4.00% |  | 4.00% |  | 4.00%
Health Care Cost Trend Rate Assumed for Next Fiscal Year |  |  | 6.75% |  |  |  |
Fair Value of Plan Assets, Beginning |  | 47.6 | $ 47.0 |  | $ 45.3 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  |  | 3.3 |  | 4.1 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  | (11.0) |  | (12.1) |  |
Accumulated Benefit Obligation |  |  | (96.9) |  | (89.5) |  |
Other Postretirement Benefits Plan [Member] | Og and E [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Benefits Paid |  |  | (8.6) |  | (9.8) |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  | 109.5 | 104.7 |  | 104.8 |  |
Service cost |  |  | 0.2 |  | 0.2 |  | $ 0.2
Interest cost |  |  | 3.2 |  | 4.3 |  | 4.2
Plan curtailments |  |  | 3.1 |  | 0.0 |  |
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant |  |  | (2.4) |  | (3.0) |  |
Actuarial losses |  |  | 4.5 |  | 2.2 |  |
Benefit Obligation, Ending |  |  | 109.5 |  | 104.7 |  | 104.8
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 42.7 | 41.9 |  | 40.6 |  |
Actual return on plans' assets |  |  | 1.1 |  | 4.0 |  |
Employer contributions |  |  | 5.9 |  | 4.1 |  |
Fair Value of Plan Assets, Ending |  |  | 42.7 |  | 41.9 |  | 40.6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  | 0.2 |  | 0.2 |  | 0.2
Interest cost |  |  | 3.2 |  | 4.3 |  | 4.2
Expected return on plan assets |  |  | (1.7) |  | (1.7) |  | (1.8)
Defined Benefit Plan, Amortization of Gain (Loss) |  |  | (2.1) |  | (2.1) |  | (3.8)
Amortization of unrecognized prior service cost | [1] |  | (6.1) |  | (6.1) |  | (6.1)
Curtailment |  |  | (1.3) |  | 0.0 |  | 0.0
Net periodic benefit cost |  |  | (1.0) |  | (1.2) |  | 0.3
Amount Attributable to Parent | [4] |  | (0.5) |  | (0.6) |  | (0.7)
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  |  | (1.5) |  | (1.8) |  | (0.4)
Capitalized Portion of Net Periodic Benefit Cost |  |  | 0.1 |  | 0.1 |  | 0.1
Fair Value of Plan Assets, Beginning |  | 42.7 | 41.9 |  | 40.6 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  |  | 2.4 |  | 3.0 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  | (8.6) |  | (9.8) |  |
Accumulated Benefit Obligation |  |  | (66.8) |  | (62.8) |  |
Other Postretirement Benefits Plan [Member] | OKLAHOMA |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Settlement cost |  |  | 1.4 |  | 0.0 |  | 0.0
Additional Pension Expense to Meet State Requirements | [5] |  | 0.2 |  | 1.0 |  | 4.4
Other Postretirement Benefits Plan [Member] | ARKANSAS |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Settlement cost |  |  | 0.1 |  | 0.0 |  | $ 0.0
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 14.2 | 12.1 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 14.2 |  | 12.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 14.2 | 12.1 |  |  |  |
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 33.4 | 34.8 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 33.4 |  | 34.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 33.4 | 34.8 |  |  |  |
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 47.6 | 46.9 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 47.6 |  | 46.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 47.6 | 46.9 |  |  |  |
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1, 2 and 3 [Member] | Og and E [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 42.7 | 41.9 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 42.7 |  | 41.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 42.7 | $ 41.9 |  |  |  |
Less Than 90% [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Fixed Income |  |  | 50.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Equity |  |  | 50.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds |  |  | 100.00% |  |  |  |
95% [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Fixed Income |  |  | 58.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Equity |  |  | 42.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds |  |  | 100.00% |  |  |  |
100% [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Fixed Income |  |  | 65.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Equity |  |  | 35.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds |  |  | 100.00% |  |  |  |
105% [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Fixed Income |  |  | 73.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Equity |  |  | 27.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds |  |  | 100.00% |  |  |  |
110% [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Fixed Income |  |  | 80.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Equity |  |  | 20.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds |  |  | 100.00% |  |  |  |
115% [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Fixed Income |  |  | 85.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Equity |  |  | 15.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds |  |  | 100.00% |  |  |  |
120% [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Fixed Income |  |  | 90.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds Equity |  |  | 10.00% |  |  |  |
Projected Benefit Obligation Funded Status Thresholds |  |  | 100.00% |  |  |  |
Domestic All-Cap/Large Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 40.00% |  |  |  |
Domestic Mid-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 15.00% |  |  |  |
Domestic Small-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 25.00% |  |  |  |
International Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 20.00% |  |  |  |
Minimum [Member] | Domestic All-Cap/Large Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 35.00% |  |  |  |
Minimum [Member] | Domestic Mid-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 5.00% |  |  |  |
Minimum [Member] | Domestic Small-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 5.00% |  |  |  |
Minimum [Member] | International Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 10.00% |  |  |  |
Maximum [Member] | Domestic All-Cap/Large Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 60.00% |  |  |  |
Maximum [Member] | Domestic Mid-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 25.00% |  |  |  |
Maximum [Member] | Domestic Small-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 30.00% |  |  |  |
Maximum [Member] | International Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  |  | 30.00% |  |  |  |
Group Retiree Medical Insurance Contract [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 33.4 | $ 34.8 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 33.4 |  | 34.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 33.4 | 34.8 |  |  |  |
Group Retiree Medical Insurance Contract [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Group Retiree Medical Insurance Contract [Member] | Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 33.4 | 34.8 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 33.4 |  | 34.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 33.4 | 34.8 |  |  |  |
U.S. common stocks [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 252.3 | 202.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 252.3 |  | 202.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 252.3 | 202.0 |  |  |  |
U.S. common stocks [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 252.3 | 202.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 252.3 |  | 202.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 252.3 | 202.0 |  |  |  |
U.S. common stocks [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
U.S. treasury notes and bonds [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6],[8] | 0.0 | [7],[9] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 134.3 | 134.8 |  |  |  |
Fair Value of Plan Assets, Ending | [9] |  | 134.3 |  | 134.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 134.3 | 134.8 |  |  |  |
U.S. treasury notes and bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 134.3 | 134.8 |  |  |  |
Fair Value of Plan Assets, Ending | [9] |  | 134.3 |  | 134.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 134.3 | 134.8 |  |  |  |
U.S. treasury notes and bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending | [9] |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 0.0 | 0.0 |  |  |  |
Mortgage-backed securities | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 29.3 | 45.8 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 29.3 |  | 45.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 29.3 | 45.8 |  |  |  |
Mortgage-backed securities | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Mortgage-backed securities | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 29.3 | 45.8 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 29.3 |  | 45.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 29.3 | 45.8 |  |  |  |
Corporate fixed income and other securities [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 116.6 | 130.5 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 116.6 |  | 130.5 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 116.6 | 130.5 |  |  |  |
Corporate fixed income and other securities [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Corporate fixed income and other securities [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 116.6 | 130.5 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 116.6 |  | 130.5 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 116.6 | 130.5 |  |  |  |
Commingled fund [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 25.4 | [6],[10] | 23.9 | [7],[11] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [11] | 25.4 | 23.9 |  |  |  |
Fair Value of Plan Assets, Ending | [11] |  | 25.4 |  | 23.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [11] | 25.4 | 23.9 |  |  |  |
Commingled fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [11] | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending | [11] |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [11] | 0.0 | 0.0 |  |  |  |
Commingled fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [11] | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending | [11] |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [11] | 0.0 | 0.0 |  |  |  |
Foreign government bonds [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 4.6 | 3.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 4.6 |  | 3.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 4.6 | 3.0 |  |  |  |
Foreign government bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Foreign government bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 4.6 | 3.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 4.6 |  | 3.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 4.6 | 3.0 |  |  |  |
Municipal bonds [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 1.8 | 1.1 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 1.8 |  | 1.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 1.8 | 1.1 |  |  |  |
Municipal bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Municipal bonds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 1.8 | 1.1 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 1.8 |  | 1.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 1.8 | 1.1 |  |  |  |
Money market funds [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 8.8 | [6] | 2.4 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 8.8 | 2.4 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 8.8 |  | 2.4 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 8.8 | 2.4 |  |  |  |
Money market funds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Money market funds [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Mutual fund [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 9.2 | 7.5 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 9.2 |  | 7.5 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 9.2 | 7.5 |  |  |  |
Mutual fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 9.2 | 7.5 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 9.2 |  | 7.5 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 9.2 | 7.5 |  |  |  |
Mutual fund [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment | [7] |  |  |  | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 22.9 |  |  |  |
Fair Value of Plan Assets, Ending |  |  |  |  | 22.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 22.9 |  |  |  |
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  |  |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 |  |  |  |
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 22.9 |  |  |  |
Fair Value of Plan Assets, Ending |  |  |  |  | 22.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 22.9 |  |  |  |
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment | [7] |  |  |  | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (10.9) |  |  |  |
Fair Value of Plan Assets, Ending |  |  |  |  | (10.9) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (10.9) |  |  |  |
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  |  |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 |  |  |  |
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (10.9) |  |  |  |
Fair Value of Plan Assets, Ending |  |  |  |  | (10.9) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (10.9) |  |  |  |
Cash collateral [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.7 | 0.6 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.7 |  | 0.6 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.7 | 0.6 |  |  |  |
Cash collateral [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.7 | 0.6 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.7 |  | 0.6 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.7 | 0.6 |  |  |  |
Cash collateral [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Receivable (foreign currency) [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.1 | 0.1 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.1 |  | 0.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.1 | 0.1 |  |  |  |
Receivable (foreign currency) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Receivable (foreign currency) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.1 | 0.1 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.1 |  | 0.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.1 | 0.1 |  |  |  |
Preferred stocks (foreign) [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 0.0 | [6] | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.6 | 0.7 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.6 |  | 0.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.6 | 0.7 |  |  |  |
Preferred stocks (foreign) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.6 | 0.7 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.6 |  | 0.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.6 | 0.7 |  |  |  |
Preferred stocks (foreign) [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 | 0.0 |  |  |  |
Total Plan investments [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment |  |  | 34.2 | [6] | 26.3 | [7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 583.7 | 564.4 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 583.7 |  | 564.4 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 583.7 | 564.4 |  |  |  |
Total Plan investments [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 397.1 | 345.6 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 397.1 |  | 345.6 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 397.1 | 345.6 |  |  |  |
Total Plan investments [Member] | Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 152.4 | 192.5 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 152.4 |  | 192.5 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 152.4 | 192.5 |  |  |  |
Receivable from broker for securities sold [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.2 |  |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 0.2 |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.2 |  |  |  |  |
Interest and dividends receivable [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 2.2 | 2.4 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 2.2 |  | 2.4 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 2.2 | 2.4 |  |  |  |
Payable to broker for securities purchased [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | (15.8) | (36.5) |  |  |  |
Fair Value of Plan Assets, Ending |  |  | (15.8) |  | (36.5) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | (15.8) | (36.5) |  |  |  |
Total Plan assets [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 570.3 | 530.3 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 570.3 |  | 530.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 570.3 | 530.3 |  |  |  |
Total Plan assets [Member] | Pension Plans, Defined Benefit [Member] | Og and E [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 420.3 | 399.1 |  |  |  |
Fair Value of Plan Assets, Ending |  |  | 420.3 |  | 399.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 420.3 | 399.1 |  |  |  |
Plan Assets Attributable to Affiliates | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | (150.0) | (131.2) |  |  |  |
Fair Value of Plan Assets, Ending |  |  | (150.0) |  | $ (131.2) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | $ (150.0) | $ (131.2) |  |  |  |
[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] | Amount paid by unconsolidated affiliates" is only applicable to OGE Energy. "Amount allocated from OGE Energy" is only applicable to OG&E.
[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] | "Amount paid by unconsolidated affiliates" is only applicable to OGE Energy. "Amount allocated from OGE Energy" is only applicable to OG&E.
[5] | Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.
[6] | GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.
[7] | GAAP allows the measurement of certain investments that do not have a readily determinable fair value at the net asset value. These investments do not consider the observability of inputs; therefore, they are not included within the fair value hierarchy.
[8] | This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher.
[9] | This category represents U.S. Treasury notes and bonds with a Moody's Investors Service rating of Aaa and Government Agency Bonds with a Moody's Investors Service rating of A1 or higher.
[10] | This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.
[11] | This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.

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