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Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022 | Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Unfunded commitments |  |  |  |  | $ 192.2
Transfers out of Level 3 | $ 0.1 | $ 5.7 | $ 0.1 | $ 5.7 |
Debt Securities, Available-for-Sale | 6,943.8 |  | 6,943.8 |  | 6,894.8
Equity Securities, FV-NI, Current | 247.0 |  | 247.0 |  | 243.2
Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total Assets | 7,240.2 |  | 7,240.2 |  | 7,183.0
Convertible debt at fair value | 46.2 |  | 46.2 |  | 43.3
Derivative Asset | 3.2 |  | 3.2 |  | 1.7
Total Liabilities |  |  |  |  | (0.4)
Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total Assets | 197.0 |  | 197.0 |  | 189.1
Convertible debt at fair value | 0.0 |  | 0.0 |  | 0.0
Derivative Asset | 0.0 |  | 0.0 |  | 0.0
Total Liabilities |  |  |  |  | 0.0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total Assets | 201.5 |  | 201.5 |  | 230.0
Convertible debt at fair value | 0.0 |  | 0.0 |  | 0.0
Derivative Asset | 0.0 |  | 0.0 |  | 0.0
Total Liabilities |  |  |  |  | 0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total Assets | 128.3 |  | 128.3 |  | 117.0
Convertible debt at fair value | 0.0 |  | 0.0 |  |
Derivative Asset | 0.0 |  | 0.0 |  | 0.0
Total Liabilities |  |  |  |  | 0.0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Total Assets | 6,713.4 |  | 6,713.4 |  | 6,646.9
Convertible debt at fair value | 46.2 |  | 46.2 |  | 43.3
Derivative Asset | 3.2 |  | 3.2 |  | 1.7
Derivative Liability |  |  |  |  | (0.4)
Total Liabilities |  |  |  |  | 0.4
Limited Liability Companies and Limited Partnerships | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 197.0 |  | 197.0 |  | 189.1
Limited Liability Companies and Limited Partnerships | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 197.0 |  | 197.0 |  | 189.1
Limited Liability Companies and Limited Partnerships | Significant Unobservable Inputs (Level 3) |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Unfunded commitments | 201.2 |  | 201.2 |  |
Limited Liability Companies and Limited Partnerships | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Limited Liability Companies and Limited Partnerships | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Limited Liability Companies and Limited Partnerships | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
U.S. Government and Government Agencies and Authorities | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 545.5 |  | 545.5 |  | 528.0
U.S. Government and Government Agencies and Authorities | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
U.S. Government and Government Agencies and Authorities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
U.S. Government and Government Agencies and Authorities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 120.0 |  | 120.0 |  | 103.6
U.S. Government and Government Agencies and Authorities | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 425.5 |  | 425.5 |  | 424.4
States and Political Subdivisions | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 1,461.0 |  | 1,461.0 |  | 1,568.9
States and Political Subdivisions | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
States and Political Subdivisions | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
States and Political Subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
States and Political Subdivisions | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 1,461.0 |  | 1,461.0 |  | 1,568.9
Foreign Governments | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 4.0 |  | 4.0 |  | 4.1
Foreign Governments | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Foreign Governments | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Foreign Governments | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Foreign Governments | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 4.0 |  | 4.0 |  | 4.1
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 3,633.4 |  | 3,633.4 |  | 3,539.4
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 187.4 |  | 187.4 |  | 216.0
Corporate Debt Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 3,446.0 |  | 3,446.0 |  | 3,323.4
Redeemable Preferred Stocks | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 7.9 |  | 7.9 |  | 8.0
Redeemable Preferred Stocks | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  |
Redeemable Preferred Stocks | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 6.7 |  | 6.7 |  |
Redeemable Preferred Stocks | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  |
Redeemable Preferred Stocks | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 1.2 |  | 1.2 |  |
Collateralized Loan Obligations | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 987.2 |  | 987.2 |  | 953.9
Collateralized Loan Obligations | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Collateralized Loan Obligations | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Collateralized Loan Obligations | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Collateralized Loan Obligations | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 987.2 |  | 987.2 |  | 953.9
Other Mortgage- and Asset-backed | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 304.8 |  | 304.8 |  | 292.5
Other Mortgage- and Asset-backed | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Other Mortgage- and Asset-backed | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 5.2 |  | 5.2 |  | 5.1
Other Mortgage- and Asset-backed | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Other Mortgage- and Asset-backed | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 299.6 |  | 299.6 |  | 287.4
Investments in Fixed Maturities | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 6,943.8 |  | 6,943.8 |  | 6,894.8
Investments in Fixed Maturities | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 0.0 |  | 0.0 |  | 0.0
Investments in Fixed Maturities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 199.3 |  | 199.3 |  | 227.9
Investments in Fixed Maturities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 120.0 |  | 120.0 |  | 103.6
Investments in Fixed Maturities | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale | 6,624.5 |  | 6,624.5 |  | 6,563.3
Preferred Stocks | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 30.0 |  | 30.0 |  | 29.0
Preferred Stocks | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Preferred Stocks | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 11.3 |  | 11.3 |  | 10.8
Preferred Stocks | Fair Value, Measurements, Recurring | Other Industries | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Preferred Stocks | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Preferred Stocks | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 1.8 |  | 1.8 |  | 1.6
Preferred Stocks | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Preferred Stocks | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Preferred Stocks | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 30.0 |  | 30.0 |  | 29.0
Preferred Stocks | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 9.5 |  | 9.5 |  | 9.2
Common Stock | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.6 |  | 0.6 |  | 0.9
Common Stock | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Common Stock | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.8 |  | 0.8 |  | 1.2
Common Stock | Fair Value, Measurements, Recurring | Other Industries | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Common Stock | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Common Stock | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.4 |  | 0.4 |  | 0.5
Common Stock | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.6 |  | 0.6 |  | 0.9
Common Stock | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.4 |  | 0.4 |  | 0.3
Common Stock | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Finance, Insurance and Real Estate |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Common Stock | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Other Industries |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.4
Exchange Traded Funds | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 7.3 |  | 7.3 |  | 12.2
Exchange Traded Funds | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Exchange Traded Funds | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Exchange Traded Funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 7.3 |  | 7.3 |  | 12.2
Exchange Traded Funds | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 0.0 |  | 0.0 |  | 0.0
Equity Securities | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 247.0 |  | 247.0 |  | 243.2
Equity Securities | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 197.0 |  | 197.0 |  | 189.1
Equity Securities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 2.2 |  | 2.2 |  | 2.1
Equity Securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | 8.3 |  | 8.3 |  | 13.4
Equity Securities | Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Current | $ 39.5 |  | $ 39.5 |  | 38.6
Designated as Hedging Instrument | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Derivative Asset |  |  |  |  | (0.4)
Designated as Hedging Instrument | Fair Value, Measurements, Recurring | Measured at Net Asset Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Derivative Liability |  |  |  |  | 0.0
Designated as Hedging Instrument | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Derivative Liability |  |  |  |  | 0.0
Designated as Hedging Instrument | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Derivative Liability |  |  |  |  | $ 0.0

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