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Fair Value Measurements - Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2017 | Dec. 31, 2016 | Sep. 30, 2016
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Catastrophe bonds trading, at fair value | $ 33.5 | $ 42.5 |
Derivatives at fair value | 8.4 | 7.2 |
Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Catastrophe bonds trading, at fair value | 30.3 |  |
Loan notes issued by variable interest entities, at fair value | (101.5) | (115.0) |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) | (2.4) | (108.4) |
Total | 7,555.6 | 7,653.6 |
Fair Value, Measurements, Recurring | Short-term investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 90.3 | 185.4 |
Fair Value, Measurements, Recurring | Equity investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 468.6 | 584.7 |
Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivatives at fair value | 8.4 | 7.2 |
Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities under derivative contracts, fair value | (2.9) | (18.4) |
Available for sale financial assets | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 5,365.4 | 5,664.6 |
Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 1,172.6 | 1,206.1 |
Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 62.1 | 119.6 |
Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 50.1 | 24.4 |
Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 2,468.4 | 2,586.5 |
Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 94.0 | 89.8 |
Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 531.7 | 488.7 |
Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 33.7 | 63.0 |
Available for sale financial assets | Fair Value, Measurements, Recurring | Non-agency commercial mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value |  | 12.6 |
Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 952.8 | 1,073.9 |
Short-term investments | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 34.4 | 145.3 |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 1,665.0 | 1,265.7 |
Catastrophe bonds trading, at fair value |  | 42.5 |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 160.6 | 82.4 |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 |  |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 32.3 | 15.5 |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 1,045.0 | 820.6 |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 2.0 |  |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 210.9 | 202.8 |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 11.1 | 14.5 |
Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 203.1 | 129.9 |
Level 1 | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Catastrophe bonds trading, at fair value | 0.0 |  |
Loan notes issued by variable interest entities, at fair value | 0.0 | 0.0 |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) | 0.0 | 0.0 |
Total | 2,318.9 | 2,411.6 |
Level 1 | Fair Value, Measurements, Recurring | Short-term investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 90.0 | 76.1 |
Level 1 | Fair Value, Measurements, Recurring | Equity investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 468.6 | 584.7 |
Level 1 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivatives at fair value | 0.0 | 0.0 |
Level 1 | Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities under derivative contracts, fair value | 0.0 | 0.0 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 1,547.8 | 1,549.8 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 1,172.6 | 1,206.1 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 375.2 | 343.7 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-agency commercial mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value |  | 0.0 |
Level 1 | Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Short-term investments | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 27.4 | 118.6 |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 185.1 | 82.4 |
Catastrophe bonds trading, at fair value |  | 0.0 |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 160.6 | 82.4 |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 |  |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 |  |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 24.5 | 0.0 |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 1 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 2 | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Catastrophe bonds trading, at fair value | 30.3 |  |
Loan notes issued by variable interest entities, at fair value | 0.0 | 0.0 |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) | 0.0 | 0.0 |
Total | 5,340.6 | 5,465.4 |
Level 2 | Fair Value, Measurements, Recurring | Short-term investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.3 | 109.3 |
Level 2 | Fair Value, Measurements, Recurring | Equity investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 2 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivatives at fair value | 8.4 | 7.2 |
Level 2 | Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities under derivative contracts, fair value | (2.9) | (18.4) |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 3,817.6 | 4,114.8 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 62.1 | 119.6 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 50.1 | 24.4 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 2,468.4 | 2,586.5 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 94.0 | 89.8 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 156.5 | 145.0 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 33.7 | 63.0 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-agency commercial mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value |  | 12.6 |
Level 2 | Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 952.8 | 1,073.9 |
Level 2 | Short-term investments | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 7.0 | 26.7 |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 1,479.9 | 1,183.3 |
Catastrophe bonds trading, at fair value |  | 42.5 |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 |  |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 32.3 | 15.5 |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 1,045.0 | 820.6 |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 2.0 |  |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 186.4 | 202.8 |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 11.1 | 14.5 |
Level 2 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 203.1 | 129.9 |
Level 3 | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Catastrophe bonds trading, at fair value | 0.0 |  |
Loan notes issued by variable interest entities, at fair value | (101.5) | (115.0) |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) | (2.4) | (108.4) | $ (2.3)
Total | 103.9 | 223.4 |
Level 3 | Fair Value, Measurements, Recurring | Short-term investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Fair Value, Measurements, Recurring | Equity investments trading, at fair value |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Fair Value, Measurements, Recurring | Derivatives at fair value, assets | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Derivatives at fair value | 0.0 | 0.0 |
Level 3 | Fair Value, Measurements, Recurring | Liabilities under derivative contracts — foreign exchange contracts | Foreign Exchange Contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liabilities under derivative contracts, fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Non-agency commercial mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value |  | 0.0 |
Level 3 | Available for sale financial assets | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Short-term investments | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Catastrophe bonds trading, at fair value |  | 0.0 |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | U.S. agency |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 |  |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Municipal |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government-backed corporate |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 |  |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Non-U.S. government |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Asset-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | 0.0 | 0.0 |
Level 3 | Held for trading financial assets, at fair value | Fair Value, Measurements, Recurring | Agency mortgage-backed |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Investments, at fair value | $ 0.0 | $ 0.0 |

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