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v3.19.3.a.u2

Retirement Plans and Postretirement Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
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 |  | $ 20.0 |  | $ 15.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
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 |  | 0.1 |  | 0.1
Effect of One Percentage Point Decrease on Service and Interest Cost Components |  | 0.0 |  | 0.0 |  | 0.0
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation |  | 0.3 |  | 0.3 |  | 0.3
Expected Future Benefit Payments, Next Twelve Months |  | 58.4 |  |  |  |
Expected Future Benefit Payments, Year Two |  | 56.8 |  |  |  |
Expected Future Benefit Payments, Year Three |  | 56.2 |  |  |  |
Expected Future Benefit Payments, Year Four |  | 55.7 |  |  |  |
Expected Future Benefit Payments, Year Five |  | 56.6 |  |  |  |
Expected Future Benefit Payments, Five Fiscal Years Thereafter |  | 249.4 |  |  |  |
Defined Contribution Plan, Cost |  | 14.4 |  | 13.2 |  | 13.2
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 |  | (14.6) |  | (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 |  | 615.9 |  | 687.5 |  |
Service cost |  | 12.9 |  | 14.9 |  | 15.5
Interest cost |  | 20.7 |  | 23.8 |  | 26.2
Plan settlements |  | (83.1) |  | (73.7) |  |
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant |  | 0.0 |  | 0.0 |  |
Actuarial losses (gains) |  | 64.3 |  | (22.0) |  |
Benefit Obligation, Ending |  | 616.1 |  | 615.9 |  | 687.5
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 522.8 |  | 635.3 |  |
Actual return on plans' assets |  | 85.2 |  | (39.2) |  |
Employer contributions |  | 20.0 |  | 15.0 |  |
Plan settlements |  | (83.1) |  | (73.7) |  |
Fair Value of Plan Assets, Ending |  | 530.3 |  | 522.8 |  | 635.3
Funded Status of Plan |  | (85.8) |  | (93.1) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Service cost |  | 12.9 |  | 14.9 |  | 15.5
Interest cost |  | 20.7 |  | 23.8 |  | 26.2
Expected return on plan assets |  | (36.1) |  | (44.1) |  | (42.6)
Defined Benefit Plan, Amortization of Gain (Loss) |  | (17.3) |  | (16.2) |  | (17.4)
Amortization of unrecognized prior service cost | [1] | 0.0 |  | 0.0 |  | (0.1)
Settlement cost |  | 27.6 |  | 25.1 |  | 15.3
Net periodic benefit cost |  | 42.4 |  | 35.9 |  | 31.7
Amount paid by unconsolidated affiliates |  | 2.9 |  | 2.5 |  | 4.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  | 39.5 |  | 33.4 |  | 27.4
Plan settlements |  | (83.1) |  | (73.7) |  |
Capitalized Portion of Net Periodic Benefit Cost |  | $ 3.6 |  | $ 3.8 |  | $ 4.4
Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 3.15% |  | 4.20% |  | 3.60%
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 |  | $ 522.8 |  | $ 635.3 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | (14.6) |  | (14.6) |  |
Pension Plans, Defined Benefit [Member] | OKLAHOMA |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Settlement cost | [2] | 17.9 |  | 22.1 |  | $ 13.2
Additional Pension Expense to Meet State Requirements | [2] | (16.1) |  | (14.1) |  | (2.3)
Pension Plans, Defined Benefit [Member] | ARKANSAS |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Settlement cost | [2] | 1.7 |  | 2.1 |  | 1.1
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 |  |  |  |
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 |  |  |  |
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 |  | 0.3 |  | 0.0 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |  |  |
Benefit Obligation, Beginning |  | 9.6 |  | 8.1 |  |
Service cost |  | 0.5 |  | 0.4 |  | 0.3
Interest cost |  | 0.4 |  | 0.3 |  | 0.3
Plan settlements |  | (1.2) |  | (2.0) |  |
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant |  | 0.0 |  | 0.0 |  |
Actuarial losses (gains) |  | 0.7 |  | 2.8 |  |
Benefit Obligation, Ending |  | 10.3 |  | 9.6 |  | 8.1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.0 |  | 0.0 |  |
Actual return on plans' assets |  | 0.0 |  | 0.0 |  |
Employer contributions |  | 1.2 |  | 2.0 |  |
Plan settlements |  | (1.2) |  | (2.0) |  |
Fair Value of Plan Assets, Ending |  | 0.0 |  | 0.0 |  | 0.0
Funded Status of Plan |  | (10.3) |  | (9.6) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Service cost |  | 0.5 |  | 0.4 |  | 0.3
Interest cost |  | 0.4 |  | 0.3 |  | 0.3
Expected return on plan assets |  | 0.0 |  | 0.0 |  | 0.0
Defined Benefit Plan, Amortization of Gain (Loss) |  | (0.5) |  | (0.7) |  | (0.4)
Amortization of unrecognized prior service cost | [1] | 0.0 |  | 0.1 |  | 0.1
Settlement cost |  | 0.5 |  | 1.0 |  | 0.0
Net periodic benefit cost |  | 1.9 |  | 2.5 |  | 1.1
Amount paid by unconsolidated affiliates |  | 0.1 |  | 0.1 |  | 0.0
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  | 1.8 |  | 2.4 |  | 1.1
Plan settlements |  | (1.2) |  | (2.0) |  |
Fair Value of Plan Assets, Beginning |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | 0.0 |  | 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 |  | (12.1) |  | (13.5) |  |
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 |  | 135.8 |  | 149.4 |  |
Service cost |  | 0.2 |  | 0.3 |  | 0.6
Interest cost |  | 5.6 |  | 5.4 |  | 7.2
Plan settlements |  | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant |  | (4.1) |  | (3.8) |  |
Actuarial losses (gains) |  | 2.9 |  | (9.6) |  |
Benefit Obligation, Ending |  | 136.5 |  | 135.8 |  | 149.4
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 45.3 |  | 50.2 |  |
Actual return on plans' assets |  | 4.6 |  | (0.6) |  |
Employer contributions |  | 5.1 |  | 5.4 |  |
Plan settlements |  | 0.0 |  | 0.0 |  |
Fair Value of Plan Assets, Ending |  | 47.0 |  | 45.3 |  | 50.2
Funded Status of Plan |  | (89.5) |  | (90.5) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Service cost |  | 0.2 |  | 0.3 |  | 0.6
Interest cost |  | 5.6 |  | 5.4 |  | 7.2
Expected return on plan assets |  | (1.9) |  | (2.0) |  | (2.2)
Defined Benefit Plan, Amortization of Gain (Loss) |  | (2.0) |  | (3.8) |  | (2.0)
Amortization of unrecognized prior service cost | [1] | (8.4) |  | (8.4) |  | (3.5)
Settlement cost |  | 0.0 |  | 0.0 |  | 0.6
Net periodic benefit cost |  | (2.5) |  | (0.9) |  | 4.7
Amount paid by unconsolidated affiliates |  | (0.6) |  | (0.5) |  | 0.3
Net Periodic Benefit Cost, Net of Unconsolidated Affiliates |  | (1.9) |  | (0.4) |  | 4.4
Plan settlements |  | 0.0 |  | 0.0 |  |
Capitalized Portion of Net Periodic Benefit Cost |  | $ 0.2 |  | $ 0.2 |  | $ 1.2
Assumptions Used Calculating Benefit Obligation, Discount Rate |  | 3.25% |  | 4.30% |  | 3.70%
Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets |  | 4.00% |  | 4.00% |  | 4.00%
Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase |  |  |  |  |  | 4.20%
Health Care Cost Trend Rate Assumed for Next Fiscal Year |  |  |  | 7.00% |  |
Fair Value of Plan Assets, Beginning |  | $ 45.3 |  | $ 50.2 |  |
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant |  | 4.1 |  | 3.8 |  |
Defined Benefit Plan, Benefit Obligation, Benefits Paid |  | (12.1) |  | (13.5) |  |
Other Postretirement Benefits Plan [Member] | OKLAHOMA |  |  |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Additional Pension Expense to Meet State Requirements | [3] | 1.0 |  | 4.4 |  | $ 6.2
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 |  | 9.8 |  |  |  |
Fair Value of Plan Assets, Ending |  | 12.1 |  | 9.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 9.8 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  | 36.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 34.8 |  | 36.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 36.0 |  |  |  |
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 |  | 45.8 |  |  |  |
Fair Value of Plan Assets, Ending |  | 46.9 |  | 45.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | $ 45.8 |  |  |  |
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 |  | $ 36.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 34.8 |  | 36.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 36.0 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  | 36.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 34.8 |  | 36.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 36.0 |  |  |  |
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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 169.3 |  |  |  |
Fair Value of Plan Assets, Ending |  | 202.0 |  | 169.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 169.3 |  |  |  |
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 |  | 169.3 |  |  |  |
Fair Value of Plan Assets, Ending |  | 202.0 |  | 169.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 169.3 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 | [4],[6] | 0.0 | [5],[7] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [7] | 137.9 |  |  |  |
Fair Value of Plan Assets, Ending | [7] | 134.8 |  | 137.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [7] | 137.9 |  |  |  |
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 | [7] | 137.9 |  |  |  |
Fair Value of Plan Assets, Ending | [7] | 134.8 |  | 137.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [7] | 137.9 |  |  |  |
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 | [7] | 0.0 |  |  |  |
Fair Value of Plan Assets, Ending | [7] | 0.0 |  | 0.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [7] | 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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 65.9 |  |  |  |
Fair Value of Plan Assets, Ending |  | 45.8 |  | 65.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 65.9 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  | 65.9 |  |  |  |
Fair Value of Plan Assets, Ending |  | 45.8 |  | 65.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 65.9 |  |  |  |
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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 143.2 |  |  |  |
Fair Value of Plan Assets, Ending |  | 130.5 |  | 143.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 143.2 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  | 143.2 |  |  |  |
Fair Value of Plan Assets, Ending |  | 130.5 |  | 143.2 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 143.2 |  |  |  |
Commingled fund [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Alternative Investment |  | 23.9 | [4],[8] | 19.7 | [5],[9] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 19.7 |  |  |  |
Fair Value of Plan Assets, Ending | [9] | 23.9 |  | 19.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning | [9] | 19.7 |  |  |  |
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 | [9] | 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 |  |  |  |
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 | [9] | 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 |  |  |  |
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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 4.4 |  |  |  |
Fair Value of Plan Assets, Ending |  | 3.0 |  | 4.4 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 4.4 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  | 4.4 |  |  |  |
Fair Value of Plan Assets, Ending |  | 3.0 |  | 4.4 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 4.4 |  |  |  |
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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.6 |  |  |  |
Fair Value of Plan Assets, Ending |  | 1.1 |  | 0.6 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.6 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  | 0.6 |  |  |  |
Fair Value of Plan Assets, Ending |  | 1.1 |  | 0.6 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.6 |  |  |  |
Money market funds [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Alternative Investment |  | 7.5 | [4] | 0.3 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.3 |  |  |  |
Fair Value of Plan Assets, Ending |  | 7.5 |  | 0.3 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 0.3 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  |  |  |
Money market funds [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Ending |  | 1.2 |  |  |  |
Money market funds [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, Ending |  | 1.2 |  |  |  |
Money market funds [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, Ending |  | 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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 8.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 2.4 |  | 8.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 8.0 |  |  |  |
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 |  | 8.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 2.4 |  | 8.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 8.0 |  |  |  |
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 |  |  |  |
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 |  |  |  |
Treasury futures, receivable [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Alternative Investment |  | 0.0 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 27.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 22.9 |  | 27.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 27.0 |  |  |  |
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 |  | 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 |  | 27.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 22.9 |  | 27.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 27.0 |  |  |  |
Treasury futures, payable [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Alternative Investment |  | 0.0 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | (20.4) |  |  |  |
Fair Value of Plan Assets, Ending |  | (10.9) |  | (20.4) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | (20.4) |  |  |  |
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 |  | 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 |  | (20.4) |  |  |  |
Fair Value of Plan Assets, Ending |  | (10.9) |  | (20.4) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | (20.4) |  |  |  |
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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 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 |  | 0.7 |  |  |  |
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 |  |  |  |
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 |  | 0.7 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 | [4] | 0.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 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 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  |  |  |
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 |  |  |  |
Preferred stocks (foreign) [Member] | Pension Plans, Defined Benefit [Member] |  |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |  |
Alternative Investment | [4] | 0.0 |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Ending |  | 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, Ending |  | 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, Ending |  | 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 |  | 31.4 | [4] | 20.0 | [5] |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 556.7 |  |  |  |
Fair Value of Plan Assets, Ending |  | 564.4 |  | 556.7 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 556.7 |  |  |  |
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 |  | 315.9 |  |  |  |
Fair Value of Plan Assets, Ending |  | 340.5 |  | 315.9 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 315.9 |  |  |  |
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 |  | 220.8 |  |  |  |
Fair Value of Plan Assets, Ending |  | 192.5 |  | 220.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 220.8 |  |  |  |
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 |  | 3.0 |  |  |  |
Fair Value of Plan Assets, Ending |  | 2.4 |  | 3.0 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | 3.0 |  |  |  |
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 |  | (36.9) |  |  |  |
Fair Value of Plan Assets, Ending |  | (36.5) |  | (36.9) |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | (36.9) |  |  |  |
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 |  | 522.8 |  |  |  |
Fair Value of Plan Assets, Ending |  | 530.3 |  | $ 522.8 |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |  |  |
Fair Value of Plan Assets, Beginning |  | $ 522.8 |  |  |  |
[1] | Unamortized prior service cost is amortized on a straight-line basis over the average remaining service period to the first eligibility age of participants who are expected to receive a benefit and are active at the date of the plan amendment.
[2] | Included in the pension regulatory asset or liability in each jurisdiction, as indicated in the regulatory assets and liabilities table in Note 1.
[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] | 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.
[5] | 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.
[6] | 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.
[7] | 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.
[8] | This category represents units of participation in a commingled fund that primarily invested in stocks of international companies and emerging markets.
[9] | 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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- Definition Projected Benefit Obligation Funded Status Thresholds + References No definition available. + Details
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- Definition Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=SL6742756-110258 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 35 -Paragraph 54B -URI http://asc.fasb.org/extlink&oid=117332851&loc=SL7495116-110257 + Details
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- 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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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- 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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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- Definition Amount of contributions received by defined benefit plan from participant which increase benefit obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- 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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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