XML 87 R68.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Retirement Plans and Postretirement Benefit Plans (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment |  |  | $ 42.9 |  |  |  |
Defined Benefit Plan, Plan Assets, Payment for Settlement |  |  | 26.4 |  |  |  |
Payment for Pension Benefits |  |  |  | $ 20.0 | $ 20.0 |  |
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 Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Plan settlements |  |  | (27.9) |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Plan settlements |  |  | (27.9) |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Net periodic benefit cost |  |  |  | $ 32.9 | 22.5 | $ 40.2 |
Plan settlements |  |  | (27.9) |  |  |  |
Effect of One Percentage Point Increase on Service and Interest Cost Components |  |  |  | 0.0 | 0.0 | 0.0 |
Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation |  |  |  | 0.1 | 0.2 | 0.2 |
Effect of One Percentage Point Decrease on Service and Interest Cost Components |  |  |  | 0.0 | 0.0 | 0.1 |
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation |  |  |  | 0.3 | 0.7 | 0.7 |
Expected Future Benefit Payments, Next Twelve Months |  | $ 65.6 |  | 65.6 |  |  |
Expected Future Benefit Payments, Year Two |  | 62.0 |  | 62.0 |  |  |
Expected Future Benefit Payments, Year Three |  | 63.4 |  | 63.4 |  |  |
Expected Future Benefit Payments, Year Four |  | 62.3 |  | 62.3 |  |  |
Expected Future Benefit Payments, Year Five |  | 61.1 |  | 61.1 |  |  |
Expected Future Benefit Payments, Five Fiscal Years Thereafter |  | 285.0 |  | 285.0 |  |  |
Defined Contribution Plan, Cost |  |  |  | 13.2 | 11.9 | 11.6 |
Net Effect of Settlement on Other Comprehensive Income and Regulatory Assets |  |  | 2.1 |  |  |  |
Pension Plans [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment |  |  |  | 0.0 | 0.0 |  |
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 |  |  |  | (14.8) | (53.8) |  |
Accumulated Benefit Obligation |  | 626.9 |  | 626.9 | 608.0 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  |  | 672.2 | 672.2 | 680.0 |  |
Service cost |  |  |  | 15.5 | 15.8 | 16.1 |
Interest cost |  |  |  | 26.2 | 25.5 | 26.1 |
Plan settlements |  |  |  | (50.2) | 0.0 |  |
Participants' contributions |  |  |  | 0.0 | 0.0 |  |
Actuarial gains (losses) |  |  |  | 38.6 | 4.7 |  |
Benefit Obligation, Ending |  | 687.5 |  | 687.5 | 672.2 | 680.0 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 595.9 | 595.9 | 581.7 |  |
Actual return on plans' assets |  |  |  | 84.4 | 48.0 |  |
Employer contributions |  |  |  | 20.0 | 20.0 |  |
Plan settlements |  |  |  | (50.2) | 0.0 |  |
Fair Value of Plan Assets, Ending |  | 635.3 |  | 635.3 | 595.9 | 581.7 |
Funded Status of Plan |  | (52.2) |  | (52.2) | (76.3) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  |  | 15.5 | 15.8 | 16.1 |
Interest cost |  |  |  | 26.2 | 25.5 | 26.1 |
Expected return on plan assets |  |  |  | (42.6) | (41.5) | (46.0) |
Defined Benefit Plan, Amortization of Gain (Loss) |  |  |  | (17.4) | (16.5) | (18.0) |
Amortization of unrecognized prior service cost | [1] |  |  | (0.1) | (0.1) | 0.4 |
Settlement |  | $ 15.3 |  | 15.3 | 0.0 | 21.7 |
Net periodic benefit cost |  |  |  | 31.7 | 16.2 | 36.3 |
Amount paid by unconsolidated affiliates |  |  |  | 4.3 | 5.1 | 4.2 |
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates | [2] |  |  | 27.4 | 11.1 | 32.1 |
Plan settlements |  |  |  | (50.2) | 0.0 |  |
Capitalized Portion of Net Periodic Benefit Cost |  |  |  | $ 4.4 | $ 4.0 | $ 5.0 |
Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 3.60% |  | 3.60% | 4.00% | 4.00% |
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 |  |  | 595.9 | $ 595.9 | $ 581.7 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  |  |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  |  | (14.8) | (53.8) |  |
Pension Plans, Defined Benefit [Member] | OKLAHOMA |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Additional Pension Expense to Meet State Requirements |  |  |  | (2.3) | 9.9 | $ (3.1) |
Pension Plans, Defined Benefit [Member] | ARKANSAS |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Settlement |  |  |  | (1.1) | (0.1) | (1.9) |
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 |  |
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 |  |
Pension Plans, Defined Benefit [Member] | U.S. common stocks [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | $ 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 237.1 | 237.1 |  |  |
Fair Value of Plan Assets, Ending |  | 225.9 |  | 225.9 | 237.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 237.1 | 237.1 |  |  |
Pension Plans, Defined Benefit [Member] | U.S. common stocks [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 |  |  | 237.1 | 237.1 |  |  |
Fair Value of Plan Assets, Ending |  | 225.9 |  | 225.9 | 237.1 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 237.1 | 237.1 |  |  |
Pension Plans, Defined Benefit [Member] | U.S. common stocks [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | U.S. treasury notes and bonds [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3],[4] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [4] |  | 122.3 | 122.3 |  |  |
Fair Value of Plan Assets, Ending | [4] | 169.7 |  | 169.7 | 122.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [4] |  | 122.3 | 122.3 |  |  |
Pension Plans, Defined Benefit [Member] | U.S. treasury notes and bonds [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 | [4] |  | 122.3 | 122.3 |  |  |
Fair Value of Plan Assets, Ending | [4] | 169.7 |  | 169.7 | 122.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [4] |  | 122.3 | 122.3 |  |  |
Pension Plans, Defined Benefit [Member] | U.S. treasury notes and bonds [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] |  | 0.0 | 0.0 |  |  |
Fair Value of Plan Assets, Ending | [4] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [4] |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Mortgage-backed securities |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 59.2 | 59.2 |  |  |
Fair Value of Plan Assets, Ending |  | 43.4 |  | 43.4 | 59.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 59.2 | 59.2 |  |  |
Pension Plans, Defined Benefit [Member] | Mortgage-backed securities | 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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Mortgage-backed securities | Fair Value, Inputs, Level 2 [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 59.2 | 59.2 |  |  |
Fair Value of Plan Assets, Ending |  | 43.4 |  | 43.4 | 59.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 59.2 | 59.2 |  |  |
Pension Plans, Defined Benefit [Member] | Corporate fixed income and other securities [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 137.6 | 137.6 |  |  |
Fair Value of Plan Assets, Ending |  | 153.8 |  | 153.8 | 137.6 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 137.6 | 137.6 |  |  |
Pension Plans, Defined Benefit [Member] | Corporate fixed income and other securities [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Corporate fixed income and other securities [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 |  |  | 137.6 | 137.6 |  |  |
Fair Value of Plan Assets, Ending |  | 153.8 |  | 153.8 | 137.6 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 137.6 | 137.6 |  |  |
Pension Plans, Defined Benefit [Member] | Commingled fund [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3],[5] | 29.9 |  | 29.9 | 23.8 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [5] |  | 23.8 | 23.8 |  |  |
Fair Value of Plan Assets, Ending | [5] | 29.9 |  | 29.9 | 23.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [5] |  | 23.8 | 23.8 |  |  |
Pension Plans, Defined Benefit [Member] | Commingled fund [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 | [5] |  | 0.0 | 0.0 |  |  |
Fair Value of Plan Assets, Ending | [5] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [5] |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Commingled fund [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 | [5] |  | 0.0 | 0.0 |  |  |
Fair Value of Plan Assets, Ending | [5] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [5] |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Foreign government bonds [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 5.2 | 5.2 |  |  |
Fair Value of Plan Assets, Ending |  | 4.0 |  | 4.0 | 5.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 5.2 | 5.2 |  |  |
Pension Plans, Defined Benefit [Member] | Foreign government bonds [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Foreign government bonds [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 |  |  | 5.2 | 5.2 |  |  |
Fair Value of Plan Assets, Ending |  | 4.0 |  | 4.0 | 5.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 5.2 | 5.2 |  |  |
Pension Plans, Defined Benefit [Member] | Municipal bonds [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 1.9 | 1.9 |  |  |
Fair Value of Plan Assets, Ending |  | 1.2 |  | 1.2 | 1.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 1.9 | 1.9 |  |  |
Pension Plans, Defined Benefit [Member] | Municipal bonds [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Municipal bonds [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 |  |  | 1.9 | 1.9 |  |  |
Fair Value of Plan Assets, Ending |  | 1.2 |  | 1.2 | 1.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 1.9 | 1.9 |  |  |
Pension Plans, Defined Benefit [Member] | Money market funds [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 4.3 |  | 4.3 | 2.2 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 2.2 | 2.2 |  |  |
Fair Value of Plan Assets, Ending |  | 4.3 |  | 4.3 | 2.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 2.2 | 2.2 |  |  |
Pension Plans, Defined Benefit [Member] | Money market funds [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Money market funds [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Mutual fund [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 9.0 | 9.0 |  |  |
Fair Value of Plan Assets, Ending |  | 7.8 |  | 7.8 | 9.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 9.0 | 9.0 |  |  |
Pension Plans, Defined Benefit [Member] | Mutual fund [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 |  |  | 9.0 | 9.0 |  |  |
Fair Value of Plan Assets, Ending |  | 7.8 |  | 7.8 | 9.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 9.0 | 9.0 |  |  |
Pension Plans, Defined Benefit [Member] | Mutual fund [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Treasury futures, receivable [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 10.7 | 10.7 |  |  |
Fair Value of Plan Assets, Ending |  | 13.4 |  | 13.4 | 10.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 10.7 | 10.7 |  |  |
Pension Plans, Defined Benefit [Member] | Treasury futures, receivable [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Treasury futures, receivable [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 |  |  | 10.7 | 10.7 |  |  |
Fair Value of Plan Assets, Ending |  | 13.4 |  | 13.4 | 10.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 10.7 | 10.7 |  |  |
Pension Plans, Defined Benefit [Member] | Treasury futures, payable [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (2.3) | (2.3) |  |  |
Fair Value of Plan Assets, Ending |  | (11.4) |  | (11.4) | (2.3) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (2.3) | (2.3) |  |  |
Pension Plans, Defined Benefit [Member] | Treasury futures, payable [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Treasury futures, payable [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 |  |  | (2.3) | (2.3) |  |  |
Fair Value of Plan Assets, Ending |  | (11.4) |  | (11.4) | (2.3) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (2.3) | (2.3) |  |  |
Pension Plans, Defined Benefit [Member] | Cash collateral [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.3 | 0.3 |  |  |
Fair Value of Plan Assets, Ending |  | 0.3 |  | 0.3 | 0.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.3 | 0.3 |  |  |
Pension Plans, Defined Benefit [Member] | Cash collateral [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 |  |  | 0.3 | 0.3 |  |  |
Fair Value of Plan Assets, Ending |  | 0.3 |  | 0.3 | 0.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.3 | 0.3 |  |  |
Pension Plans, Defined Benefit [Member] | Cash collateral [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Receivable (foreign currency) [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 0.0 |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.2 | 0.2 |  |  |
Fair Value of Plan Assets, Ending |  | 0.1 |  | 0.1 | 0.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.2 | 0.2 |  |  |
Pension Plans, Defined Benefit [Member] | Receivable (foreign currency) [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Receivable (foreign currency) [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 |  |  | 0.2 | 0.2 |  |  |
Fair Value of Plan Assets, Ending |  | 0.1 |  | 0.1 | 0.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.2 | 0.2 |  |  |
Pension Plans, Defined Benefit [Member] | Total Plan investments [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Alternative Investment, Fair Value Disclosure | [3] | 34.2 |  | 34.2 | 26.0 |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 607.2 | 607.2 |  |  |
Fair Value of Plan Assets, Ending |  | 642.4 |  | 642.4 | 607.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 607.2 | 607.2 |  |  |
Pension Plans, Defined Benefit [Member] | Total Plan investments [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 |  |  | 368.7 | 368.7 |  |  |
Fair Value of Plan Assets, Ending |  | 403.7 |  | 403.7 | 368.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 368.7 | 368.7 |  |  |
Pension Plans, Defined Benefit [Member] | Total Plan investments [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 |  |  | 212.5 | 212.5 |  |  |
Fair Value of Plan Assets, Ending |  | 204.5 |  | 204.5 | 212.5 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 212.5 | 212.5 |  |  |
Pension Plans, Defined Benefit [Member] | Receivable from broker for securities sold [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 | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 |  |  |
Pension Plans, Defined Benefit [Member] | Interest and dividends receivable [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 3.0 | 3.0 |  |  |
Fair Value of Plan Assets, Ending |  | 3.2 |  | 3.2 | 3.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 3.0 | 3.0 |  |  |
Pension Plans, Defined Benefit [Member] | Payable to broker for securities purchased [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (14.3) | (14.3) |  |  |
Fair Value of Plan Assets, Ending |  | (10.3) |  | (10.3) | (14.3) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | (14.3) | (14.3) |  |  |
Pension Plans, Defined Benefit [Member] | Total Plan assets [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 595.9 | 595.9 |  |  |
Fair Value of Plan Assets, Ending |  | 635.3 |  | 635.3 | 595.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 595.9 | 595.9 |  |  |
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 |  |  |  | (0.2) | 0.0 |  |
Accumulated Benefit Obligation |  | 7.5 |  | 7.5 | 6.1 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  |  | 7.0 | 7.0 | 25.1 |  |
Service cost |  |  |  | 0.3 | 0.3 | 1.3 |
Interest cost |  |  |  | 0.3 | 0.4 | 0.7 |
Plan settlements |  |  |  | 0.0 | (20.6) |  |
Participants' contributions |  |  |  | 0.0 | 0.0 |  |
Actuarial gains (losses) |  |  |  | 0.7 | 1.8 |  |
Benefit Obligation, Ending |  | 8.1 |  | 8.1 | 7.0 | 25.1 |
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 |  |  |  | 0.2 | 20.6 |  |
Plan settlements |  |  |  | 0.0 | (20.6) |  |
Fair Value of Plan Assets, Ending |  | 0.0 |  | 0.0 | 0.0 | 0.0 |
Funded Status of Plan |  | (8.1) |  | (8.1) | (7.0) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  |  | 0.3 | 0.3 | 1.3 |
Interest cost |  |  |  | 0.3 | 0.4 | 0.7 |
Expected return on plan assets |  |  |  | 0.0 | 0.0 | 0.0 |
Defined Benefit Plan, Amortization of Gain (Loss) |  |  |  | (0.4) | (0.7) | (0.6) |
Amortization of unrecognized prior service cost | [1] |  |  | 0.1 | 0.1 | 0.1 |
Settlement |  |  |  | 0.0 | 8.6 | 0.0 |
Net periodic benefit cost |  |  |  | 1.1 | 10.1 | 2.7 |
Amount paid by unconsolidated affiliates |  |  |  | 0.0 | 0.3 | 0.1 |
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates | [2] |  |  | 1.1 | 9.8 | 2.6 |
Plan settlements |  |  |  | 0.0 | (20.6) |  |
Fair Value of Plan Assets, Beginning |  |  | 0.0 | 0.0 | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  |  |  | 0.0 | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  |  | (0.2) | 0.0 |  |
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 |  |  |  | (15.7) | (15.7) |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |  |
Benefit Obligation, Beginning |  |  | 215.9 | 215.9 | 225.3 |  |
Service cost |  |  |  | 0.6 | 0.8 | 1.5 |
Interest cost |  |  |  | 7.2 | 9.5 | 10.3 |
Plan settlements |  |  |  | (28.1) | 0.0 |  |
Participants' contributions |  |  |  | 3.5 | 3.6 |  |
Actuarial gains (losses) |  |  |  | 5.6 | (7.6) |  |
Benefit Obligation, Ending |  | 149.4 |  | 149.4 | 215.9 | 225.3 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 53.1 | 53.1 | 55.3 |  |
Actual return on plans' assets |  |  |  | 2.8 | 2.0 |  |
Employer contributions |  |  |  | 34.6 | 7.9 |  |
Plan settlements |  |  |  | (28.1) | 0.0 |  |
Fair Value of Plan Assets, Ending |  | 50.2 |  | 50.2 | 53.1 | 55.3 |
Funded Status of Plan |  | $ (99.2) |  | (99.2) | (162.8) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Service cost |  |  |  | 0.6 | 0.8 | 1.5 |
Interest cost |  |  |  | 7.2 | 9.5 | 10.3 |
Expected return on plan assets |  |  |  | (2.2) | (2.3) | (2.4) |
Defined Benefit Plan, Amortization of Gain (Loss) |  |  |  | (2.0) | (2.6) | (13.9) |
Amortization of unrecognized prior service cost | [1] |  |  | (3.5) | (8.8) | (16.5) |
Settlement |  |  |  | 0.6 | 0.0 | 0.0 |
Net periodic benefit cost |  |  |  | 4.7 | 1.8 | 6.8 |
Amount paid by unconsolidated affiliates |  |  |  | 0.3 | 0.2 | 1.3 |
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates | [2] |  |  | 4.4 | 1.6 | 5.5 |
Plan settlements |  |  |  | (28.1) | 0.0 |  |
Capitalized Portion of Net Periodic Benefit Cost |  |  |  | $ 1.2 | $ 0.8 | $ 1.9 |
Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 3.70% |  | 3.70% | 4.20% | 4.25% |
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 |  | 7.50% |  | 7.50% | 6.75% | 6.10% | 6.50%
Ultimate Health Care Cost Trend Rate |  | 4.50% |  | 4.50% | 4.50% | 4.50% |
Year that Rate Reaches Ultimate Trend Rate |  |  |  | 2030 | 2026 | 2026 |
Fair Value of Plan Assets, Beginning |  |  | 53.1 | $ 53.1 | $ 55.3 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  |  |  | 3.5 | 3.6 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  |  |  | (15.7) | (15.7) |  |
Other Postretirement Benefits Plan [Member] | OKLAHOMA |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Additional Postretirement Medical Expense to Meet State Requirements |  |  |  | 6.2 | 7.9 | $ 5.8 |
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 |  |  | 8.4 | 8.4 |  |  |
Fair Value of Plan Assets, Ending |  | $ 10.0 |  | 10.0 | 8.4 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | 8.4 | 8.4 |  |  |
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 | 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 |  |  | 44.7 | 44.7 |  |  |
Fair Value of Plan Assets, Ending |  | $ 40.2 |  | 40.2 | 44.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  |  | $ 44.7 | 44.7 |  |  |
Restoration of Retirement Income Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment |  |  |  | 0.0 | 0.0 |  |
Postretirement Benefit Plan [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment |  |  |  | $ (39.6) | $ 0.0 |  |
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% |  | 40.00% |  |  |
Domestic Mid-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  | 15.00% |  | 15.00% |  |  |
Domestic Small-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  | 25.00% |  | 25.00% |  |  |
International Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |  |
Target Plan Asset Allocations |  | 20.00% |  | 20.00% |  |  |
Minimum [Member] | Domestic All-Cap/Large Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 0.35 |  |  |
Minimum [Member] | Domestic Mid-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 0.05 |  |  |
Minimum [Member] | Domestic Small-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 0.05 |  |  |
Minimum [Member] | International Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 0.1 |  |  |
Maximum [Member] | Domestic All-Cap/Large Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 0.6 |  |  |
Maximum [Member] | Domestic Mid-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 0.25 |  |  |
Maximum [Member] | Domestic Small-Cap Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 0.3 |  |  |
Maximum [Member] | International Equity [Member] |  |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |  |
Defined Benefit Plan, Target Allocation Percentage |  |  |  | 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] | In addition to the $32.9 million, $22.5 million and $40.2 million of net periodic benefit cost recognized in 2017, 2016 and 2015, respectively, OG&E recognized the following: •a change in pension expense in 2017, 2016 and 2015 of $(2.3) million, $9.9 million and $(3.1) million, respectively, to maintain the allowable amount to be recovered for pension expense in the Oklahoma jurisdiction, which are included in the Pension tracker regulatory asset or liability (see Note 1); •an increase in postretirement medical expense in 2017, 2016 and 2015 of $6.2 million, $7.9 million and $5.8 million, respectively, to maintain the allowable amount to be recovered for postretirement medical expense in the Oklahoma jurisdiction which are included in the Pension tracker regulatory asset or liability (see Note 1); and •a deferral of pension expense in 2017, 2016 and 2015 of $1.1 million, $0.1 million and $1.9 million related to the Arkansas jurisdictional portion of the pension settlement charge of $15.3 million, $8.6 million and $21.7 million, respectively.
[3] | 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.
[4] | This category represents U.S. Treasury notes and bonds with a Moody's Investors Services rating of Aaa and Government Agency Bonds with a Moody's Investors Services rating of A1 or higher.
[5] | This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.

X
- Definition Additional Pension Expense to Meet State Requirements + References No definition available. + Details
Name: | oge_AdditionalPensionExpenseToMeetStateRequirements
Namespace Prefix: | oge_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Additional Postretirement Medical Expense to Meet State Requirements + References No definition available. + Details
Name: | oge_AdditionalPostretirementMedicalExpenseToMeetStateRequirements
Namespace Prefix: | oge_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount Attributable to Unconsolidated Affiliates + References No definition available. + Details
Name: | oge_AmountAttributabletoUnconsolidatedAffiliates
Namespace Prefix: | oge_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Capitalized Portion of Net Periodic Benefit Cost + References No definition available. + Details
Name: | oge_CapitalizedPortionOfNetPeriodicBenefitCost
Namespace Prefix: | oge_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined Benefit Plan, Net Periodic Benefit Cost, Net of Unconsolidated Affiliates + References No definition available. + Details
Name: | oge_DefinedBenefitPlanNetPeriodicBenefitCostNetOfUnconsolidatedAffiliates
Namespace Prefix: | oge_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Net Effect of Settlement on Other Comprehensive Income and Regulatory Assets + References No definition available. + Details
Name: | oge_NetEffectofSettlementonOtherComprehensiveIncomeandRegulatoryAssets
Namespace Prefix: | oge_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Projected Benefit Obligation Funded Status Thresholds + References No definition available. + Details
Name: | oge_ProjectedBenefitObligationFundedStatusThresholds
Namespace Prefix: | oge_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Projected Benefit Obligation Funded Status Thresholds Equity + References No definition available. + Details
Name: | oge_ProjectedBenefitObligationFundedStatusThresholdsEquity
Namespace Prefix: | oge_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Projected Benefit Obligation Funded Status Thresholds Fixed Income + References No definition available. + Details
Name: | oge_ProjectedBenefitObligationFundedStatusThresholdsFixedIncome
Namespace Prefix: | oge_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + Details
Name: | us-gaap_AlternativeInvestmentsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanActuarialGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanBenefitObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of contributions received by defined benefit plan from participant which increase benefit obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanBenefitObligationContributionsByPlanParticipant
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(ii) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of decrease in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point decrease in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of increase in accumulated postretirement benefit obligation from one-percentage-point increase in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of increase in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point increase in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 + Details
Name: | us-gaap_DefinedBenefitPlanFundedStatusOfPlan
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of cost recognized for passage of time related to defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanInterestCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(7) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAmendments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of contributions received by defined benefit plan from participant which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAssetsContributionsByPlanParticipant
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(7) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanServiceCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(10) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(ii) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(8) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanSettlementsPlanAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Description of target allocation percentages, or range of percentages, considering the major categories of plan assets as of the latest statement of financial position presented (on a weighted-average basis for employers with more than one plan) that are pertinent to an understanding of the plan investment policies and strategies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920 + Details
Name: | us-gaap_DefinedBenefitPlanTargetAllocationPercentage
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Ultimate trend rate for health care cost for defined benefit postretirement plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Year ultimate health care cost trend rate is expected to be reached, in CCYY format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanYearHealthCareCostTrendRateReachesUltimateTrendRate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:gYearItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of payment for pension benefits. Excludes other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585 + Details
Name: | us-gaap_PensionContributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=oge_PensionPlansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_EntityByLocationAxis=stpr_OK
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_EntityByLocationAxis=stpr_AR
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_USCommonStocksMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_EquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_MunicipalBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=us-gaap_MutualFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_TreasuryfuturesreceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_TreasuryfuturespayableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_CashCollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_ReceivableForeignCurrencyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_TotalPlanInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_ReceivableFromBrokerForSecuritiesSoldMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_InterestAndDividendsReceivableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_PayableToBrokerForSecuritiesPurchasedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSecuritiesSeriesAxis=oge_TotalPlanAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=oge_RestorationOfRetirementIncomePlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=oge_PostretirementBenefitPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_LessThan90Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_A95Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_A100Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_A105Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_A110Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_A115Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_A120Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_DomesticAllCaplargeCapEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_DomesticMidCapEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_DomesticSmallCapEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=oge_InternationalEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |