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Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | $ 508.6 |
Fair Value of Plan Assets (Period End) | 562.5 | $ 508.6
Investment funds |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 18.0 |
Fair Value of Plan Assets (Period End) | 19.3 | 18.0
Limited partnerships |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 25.6 |
Fair Value of Plan Assets (Period End) | 25.9 | 25.6
Fixed income securities |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 19.6 |
Fair Value of Plan Assets (Period End) | 22.7 | 19.6
Insurance contracts |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 5.5 |
Fair Value of Plan Assets (Period End) | 3.6 | 5.5
Other plan assets |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 27.8 |
Fair Value of Plan Assets (Period End) | 28.9 | 27.8
Total plan assets subject to leveling |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 96.5 |
Fair Value of Plan Assets (Period End) | 100.4 | 96.5
Investments measured at net asset value |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 412.1 |
Fair Value of Plan Assets (Period End) | 462.1 | 412.1
Level 1 | Investment funds |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 18.0 |
Fair Value of Plan Assets (Period End) | 19.3 | 18.0
Level 1 | Limited partnerships |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 1 | Fixed income securities |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 19.6 |
Fair Value of Plan Assets (Period End) | 22.7 | 19.6
Level 1 | Insurance contracts |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 1 | Other plan assets |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 27.8 |
Fair Value of Plan Assets (Period End) | 28.9 | 27.8
Level 1 | Total plan assets subject to leveling |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 65.4 |
Fair Value of Plan Assets (Period End) | 70.9 | 65.4
Level 2 | Investment funds |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 2 | Limited partnerships |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 2 | Fixed income securities |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 2 | Insurance contracts |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 5.5 |
Fair Value of Plan Assets (Period End) | 3.6 | 5.5
Level 2 | Other plan assets |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 2 | Total plan assets subject to leveling |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 5.5 |
Fair Value of Plan Assets (Period End) | 3.6 | 5.5
Level 3 | Investment funds |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 3 | Limited partnerships |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 25.6 | 25.6
Actual return on plan assets | 0.3 | 0.0
Fair Value of Plan Assets (Period End) | 25.9 | 25.6
Level 3 | Fixed income securities |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 3 | Insurance contracts |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 3 | Other plan assets |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 0.0 |
Fair Value of Plan Assets (Period End) | 0.0 | 0.0
Level 3 | Total plan assets subject to leveling |  |
Fair value assets and liabilities measured on recurring basis |  |
Fair Value of Plan Assets (Period Start) | 25.6 |
Fair Value of Plan Assets (Period End) | $ 25.9 | $ 25.6

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