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Investment Securities (Fair Value Measurement by Level) (Details) $ in Millions | Jun. 30, 2019 USD ($) Investment | Dec. 31, 2018 USD ($) Investment | Jun. 30, 2018 USD ($) | Dec. 31, 2017 USD ($)
--- | --- | --- | --- | ---
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 2,483.0 | $ 2,328.7 | $ 2,275.4 | $ 3,208.3
Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 684.5 | 842.6 | 765.3 | 890.4
Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 1,134.1 | $ 1,160.5 | 1,254.6 | 2,105.4
Common Stock |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Number of hedge funds | Investment | 2 | 2 |  |
Debt securities issued by corporations |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 457.8 | $ 510.5 |  |
Mortgage-backed and asset-backed securities |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 169.4 | 133.5 |  |
Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 169.4 | 133.5 |  |
Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Other long-term investments | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 458.0 | 138.7 | 114.9 | 77.2
Hedge and private equity funds included in other long-term investments | NAV |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 206.4 | 186.9 | 140.6 | 135.3
Fair value measured on a recurring basis |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 2,670.1 | 2,542.9 |  |
Fair value measured on a recurring basis | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 854.3 | 1,047.0 |  |
Fair value measured on a recurring basis | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 1,151.4 | 1,170.3 |  |
Fair value measured on a recurring basis | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 458.0 | 138.7 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 184.8 | 153.2 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 184.8 | 153.2 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 457.8 | 510.5 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 457.8 | 510.5 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 134.3 | 143.4 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 134.3 | 143.4 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 60.9 | 55.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 60.9 | 55.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 55.5 | 47.6 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 55.5 | 47.6 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 48.6 | 60.5 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 48.6 | 60.5 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 48.4 | 57.6 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 48.4 | 57.6 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 48.0 | 68.5 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 48.0 | 68.5 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 26.0 | 31.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 26.0 | 31.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 19.9 | 19.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 19.9 | 19.8 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 16.2 | 26.3 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 16.2 | 26.3 |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 169.4 | 133.5 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [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 |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 169.4 | 133.5 |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Municipal obligations |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 297.4 | 280.3 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 297.4 | 280.3 |  |
Fair value measured on a recurring basis | Municipal obligations | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Fixed maturity investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 1,109.4 | 1,077.5 |  |
Fair value measured on a recurring basis | Fixed maturity investments | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 184.8 | 153.2 |  |
Fair value measured on a recurring basis | Fixed maturity investments | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 924.6 | 924.3 |  |
Fair value measured on a recurring basis | Fixed maturity investments | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Short-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Short-term investments, at fair value | 187.1 | 214.2 |  |
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Short-term investments, at fair value | 169.8 | 204.4 | $ 321.7 | $ 176.1
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Short-term investments, at fair value | 17.3 | 9.8 |  |
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Short-term investments, at fair value | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Financials |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 13.5 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 13.5 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 14.0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 14.0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Health Care | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 11.4 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 11.4 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Technology |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 7.4 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 7.4 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Energy |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 4.1 |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 4.1 |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 6.2 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 6.2 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 12.7 |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 12.7 |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Materials |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 3.1 |  |
Fair value measured on a recurring basis | Common equity securities | Materials | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 3.1 |  |
Fair value measured on a recurring basis | Common equity securities | Materials | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Materials | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments |  | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 513.1 | 675.3 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 499.7 | 617.0 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 13.4 | 58.3 |  |
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Other |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 196.1 | 177.9 |  |
Fair value measured on a recurring basis | Common equity securities | Other | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Other | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 196.1 | 177.9 |  |
Fair value measured on a recurring basis | Common equity securities | Other | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 709.2 | 925.6 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 499.7 | 689.4 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 209.5 | 236.2 |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 | 0.0 |  |
Fair value measured on a recurring basis | Other long-term investments |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 458.0 | 138.7 |  |
Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 |  |  |
Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | 0.0 |  |  |
Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs |  |  |  |
Debt and Equity Securities, FV-NI [Line Items] |  |  |  |
Fair value investments | $ 458.0 | $ 138.7 |  |

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