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Investment Securities (Fair Value Measurement by Level) (Details) $ in Millions | Sep. 30, 2017 USD ($) Investment | Dec. 31, 2016 USD ($) Investment | Sep. 30, 2016 USD ($) Investment | Dec. 31, 2015 USD ($)
--- | --- | --- | --- | ---
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | $ 2,509.4 | $ 2,547.3 | $ 2,406.9 | $ 1,543.5
Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 733.6 | 279.5 | 191.4 | 789.0
Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | $ 1,525.2 | $ 2,093.8 | 2,011.6 | 585.6
Common Stock [Member] |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Number of hedge funds | Investment | 2 | 1 |  |
Debt securities issued by corporations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | $ 625.0 | $ 746.3 |  |
Mortgage-backed and asset-backed securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 387.9 | 979.8 |  |
Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 387.9 | 979.8 |  |
Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fixed maturity investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | $ 5.6 | 0.0 | $ 2.1 | 0.0
Number of hedge funds | Investment | 2 |  | 2 |
Other long-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | $ 90.1 | 91.4 | $ 106.5 | 103.6
Hedge and private equity funds included in other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Other long-term investments | 154.9 | 82.6 |  |
Hedge and private equity funds included in other long-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 154.9 | 82.6 | $ 95.3 | $ 65.3
Fair value measured on a recurring basis |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 3,141.0 | 2,639.7 |  |
Fair value measured on a recurring basis | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,498.1 | 441.7 |  |
Fair value measured on a recurring basis | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,547.2 | 2,106.6 |  |
Fair value measured on a recurring basis | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 95.7 | 91.4 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 217.8 | 111.0 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 217.8 | 101.5 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 9.5 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 625.0 | 746.3 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 619.4 | 746.3 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 5.6 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 121.9 | 190.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 121.9 | 190.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 109.3 | 140.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 109.3 | 140.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 85.6 | 114.9 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 85.6 | 114.9 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 81.7 | 72.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 81.7 | 72.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 68.6 | 65.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 68.6 | 65.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 55.6 | 79.7 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 50.0 | 79.7 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 5.6 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 52.0 | 48.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 52.0 | 48.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 38.3 | 28.2 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 38.3 | 28.2 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 12.0 | 6.1 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 12.0 | 6.1 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 387.9 | 979.8 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 387.9 | 979.8 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Municipal obligations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 254.7 | 238.5 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 254.7 | 238.5 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 4.6 | 12.1 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 4.6 | 12.1 |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Fixed maturity investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,490.0 | 2,087.7 |  |
Fair value measured on a recurring basis | Fixed maturity investments | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 217.8 | 101.5 |  |
Fair value measured on a recurring basis | Fixed maturity investments | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 1,266.6 | 1,986.2 |  |
Fair value measured on a recurring basis | Fixed maturity investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 5.6 | 0.0 |  |
Fair value measured on a recurring basis | Short-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 786.5 | 175.0 |  |
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 764.5 | 162.3 |  |
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 22.0 | 12.7 |  |
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 13.0 | 8.6 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 13.0 | 8.6 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 17.1 | 13.9 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 17.1 | 13.9 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 10.3 | 7.0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 10.3 | 7.0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Financials |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 14.9 | 7.7 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 14.9 | 7.7 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Technology |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 11.7 | 7.3 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 11.7 | 7.3 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 10.2 | 1.5 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 10.2 | 1.5 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Energy |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 4.0 | 2.5 |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 4.0 | 2.5 |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 492.5 | 157.2 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 434.6 | 129.4 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 57.9 | 27.8 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Other(3) |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 200.7 | 79.9 |  |
Fair value measured on a recurring basis | Common equity securities | Other(3) | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Other(3) | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 200.7 | 79.9 |  |
Fair value measured on a recurring basis | Common equity securities | Other(3) | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 774.4 | 285.6 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 515.8 | 177.9 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 258.6 | 107.7 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 90.1 | 91.4 |  |
Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments | 90.1 | 91.4 |  |
Forward Contracts | Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Derivative, fair value, net | $ (15.4) | (1.2) |  |
Star & Shield Insurance Exchange | Fixed maturity investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments |  | 6.6 |  |
Star & Shield Insurance Exchange | Short-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Fair value investments |  | $ 0.1 |  |

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