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Investment Securities (Fair Value Measurement by Level) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015 | Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Percentage of Investments Recorded at Fair Value |  |  | 91.00% |  |  |
Equity in earnings of unconsolidated affiliates, net of tax | $ 0.0 | $ 3.9 | $ 0.0 | $ 18.0 |  |
Fair value investments | 4,900.2 | 3,365.4 | 4,900.2 | 3,365.4 | $ 4,050.9 | $ 3,343.6
Other Investments | 351.4 |  | 351.4 |  | 315.8 |
Short-term investments, at amortized cost (which approximates fair value) | 305.6 |  | 305.6 |  | 211.2 |
Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 412.4 | 418.2 | 412.4 | 418.2 | 1,152.2 | 550.6
Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 4,044.8 | 2,561.6 | 4,044.8 | 2,561.6 | 2,531.4 | 2,372.9
Debt securities issued by corporations |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 1,229.4 |  | 1,229.4 |  | 1,000.0 |
Mortgage-backed and asset-backed securities |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 2,414.5 |  | 2,414.5 |  | 1,167.0 |
Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 2,378.5 |  | 2,378.5 |  | 1,167.0 |
Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 36.0 |  | 36.0 |  | 0.0 |
Fixed maturity investments. | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 107.6 | 70.3 | 107.6 | 70.3 | 70.0 | 76.4
Common equity securities | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 | 34.2 | 0.0 | 34.2 | 0.0 | 39.5
Other long-term investments | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 192.4 | 133.7 | 192.4 | 133.7 | 169.5 | 126.9
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 | 143.0 |  | 143.0 |  | 127.8 |
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 | 143.0 | 147.4 | 143.0 | 147.4 | 127.8 | 177.3
Fair value measured on a recurring basis |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 5,062.8 |  | 5,062.8 |  | 4,134.4 |
Fair value measured on a recurring basis | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 691.0 |  | 691.0 |  | 1,363.5 |
Fair value measured on a recurring basis | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 4,071.8 |  | 4,071.8 |  | 2,531.4 |
Fair value measured on a recurring basis | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 300.0 |  | 300.0 |  | 239.5 |
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 | 97.0 |  | 97.0 |  | 160.0 |
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 | 87.5 |  | 87.5 |  | 133.4 |
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 | 9.5 |  | 9.5 |  | 26.6 |
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 |  | 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 | 1,229.4 |  | 1,229.4 |  | 1,000.0 |
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 |  | 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 | 1,229.4 |  | 1,229.4 |  | 1,000.0 |
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 | 0.0 |  | 0.0 |  | 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 | 340.5 |  | 340.5 |  | 253.3 |
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 |  | 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 | 340.5 |  | 340.5 |  | 253.3 |
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 |  | 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 | 132.2 |  | 132.2 |  | 135.6 |
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 |  | 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 | 132.2 |  | 132.2 |  | 135.6 |
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 |  | 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 | 170.8 |  | 170.8 |  | 175.9 |
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 |  | 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 | 170.8 |  | 170.8 |  | 175.9 |
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 | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 89.4 |  | 89.4 |  | 49.2 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 89.4 |  | 89.4 |  | 49.2 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 193.3 |  | 193.3 |  | 151.3 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 193.3 |  | 193.3 |  | 151.3 |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 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 | 53.6 |  | 53.6 |  | 82.0 |
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 |  | 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 | 53.6 |  | 53.6 |  | 82.0 |
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 |  | 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 | 79.6 |  | 79.6 |  | 60.0 |
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 |  | 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 | 79.6 |  | 79.6 |  | 60.0 |
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 |  | 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 | 97.1 |  | 97.1 |  | 61.5 |
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 |  | 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 | 97.1 |  | 97.1 |  | 61.5 |
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 |  | 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 | 72.9 |  | 72.9 |  | 31.2 |
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 |  | 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 | 72.9 |  | 72.9 |  | 31.2 |
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 |  | 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 | 2,414.5 |  | 2,414.5 |  | 1,167.0 |
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 |  | 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 | 2,378.5 |  | 2,378.5 |  | 1,167.0 |
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 | 36.0 |  | 36.0 |  | 0.0 |
Fair value measured on a recurring basis | Municipal obligations |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 312.3 |  | 312.3 |  | 228.8 |
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 |  | 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 | 312.3 |  | 312.3 |  | 228.8 |
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 |  | 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 | 1.2 |  | 1.2 |  | 1.2 |
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 | 0.6 |  | 0.6 |  | 0.6 |
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 | 0.6 |  | 0.6 |  | 0.6 |
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 |  | 0.0 |
Fair value measured on a recurring basis | Preferred Stock |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 85.4 |  | 85.4 |  | 82.7 |
Fair value measured on a recurring basis | Preferred Stock | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Preferred Stock | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 13.8 |  | 13.8 |  | 12.7 |
Fair value measured on a recurring basis | Preferred Stock | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 71.6 |  | 71.6 |  | 70.0 |
Fair value measured on a recurring basis | Fixed maturity investments. |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 4,139.8 |  | 4,139.8 |  | 2,639.7 |
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 | 88.1 |  | 88.1 |  | 134.0 |
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 | 3,944.1 |  | 3,944.1 |  | 2,435.7 |
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 | 107.6 |  | 107.6 |  | 70.0 |
Fair value measured on a recurring basis | Short-term investments |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 305.6 |  | 305.6 |  | 211.3 |
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 | 278.6 |  | 278.6 |  | 211.3 |
Short-term investments, at amortized cost (which approximates fair value) |  | 325.0 |  | 325.0 | 211.3 | 376.8
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 | 27.0 |  | 27.0 |  | 0.0 |
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 |  | 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 | 111.2 |  | 111.2 |  | 70.0 |
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 | 111.2 |  | 111.2 |  | 70.0 |
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 |  | 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 |  | 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 | 11.1 |  | 11.1 |  | 26.6 |
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 | 11.1 |  | 11.1 |  | 26.6 |
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 |  | 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 |  | 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 | 11.4 |  | 11.4 |  | 653.2 |
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 | 11.4 |  | 11.4 |  | 653.2 |
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 |  | 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 |  | 0.0 |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 33.3 |  | 33.3 |  | 43.7 |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 33.3 |  | 33.3 |  | 43.7 |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 33.2 |  | 33.2 |  | 35.7 |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 33.2 |  | 33.2 |  | 35.7 |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 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 | 5.5 |  | 5.5 |  |  |
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 | 5.5 |  | 5.5 |  |  |
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 | Technology |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 28.1 |  | 28.1 |  | 27.0 |
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 | 28.1 |  | 28.1 |  | 27.0 |
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 |  | 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 |  | 0.0 |
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
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Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 90.5 |  | 90.5 |  | 162.0 |
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 22.7 |  | 22.7 |  | 21.3 |
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Common equity securities | Other: |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 78.0 |  | 78.0 |  | 74.4 |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 1 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 0.0 |  | 0.0 |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 2 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 78.0 |  | 78.0 |  | 74.4 |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 3 Inputs |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Fair value investments | 0.0 |  | 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 | 425.0 |  | 425.0 |  | 1,113.9 |
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 | 324.3 |  | 324.3 |  | 1,018.2 |
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 | 100.7 |  | 100.7 |  | 95.7 |
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 |  | 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 | 192.4 |  | 192.4 |  | 169.5 |
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 |  | 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 |  | 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 | 192.4 |  | 192.4 |  | 169.5 |
Carrying value of investment accounted for using the equity method | 3.2 | 3.9 | 3.2 | 3.9 | 3.8 | 5.2
Affordable Housing Development Fund [Member] |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Other Investments | 12.8 | 15.2 | 12.8 | 15.2 | 14.7 | 16.8
Affordable Housing Development Fund [Member] | Fair value measured on a recurring basis | Other long-term investments |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Other Investments | 12.8 |  | 12.8 |  | 14.7 |
Star & Shield Insurance Exchange |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Trading Securities Debt Reclassified to Assets Held-for-sale | 8.3 | $ 9.7 | 8.3 | $ 9.7 | 9.5 | $ 10.1
Star & Shield Insurance Exchange | Short-term investments |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
Trading Securities Debt Reclassified to Assets Held-for-sale | $ 0.1 |  | $ 0.1 |  | $ 0.1 |
Surplus Note |  |  |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |
RBC Score |  |  | 250.00% |  | 250.00% |

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