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Fair Value Measurements - Financial Assets Measured on Recurring Basis (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Catastrophe Bonds, Fair Value Disclosure | $ 18.8 | $ 29.4
Derivatives at fair value | 26.8 | 12.9
Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) |  | 0.0
Total | 5,767.6 | 6,629.2
Recurring | Derivatives at fair value | Foreign exchange contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value | 26.8 | 12.9
Recurring | Derivatives at fair value | Interest rate swap |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value |  | (78.3)
Recurring | Liabilities under derivative contracts | Foreign exchange contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Liabilities under derivative contracts, fair value | (13.6) | (8.9)
Recurring | Total fixed income securities — Available for sale | Non-agency commercial mortgage-backed securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 2.3 |
Recurring | Fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 4,348.1 | 4,958.2
Recurring | Short-term investments |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 87.8 | 117.6
Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 855.6 | 1,128.8
Privately-held Investments, at fair value | 299.3 | 279.7
Catastrophe Bonds, Fair Value Disclosure | 18.8 | 28.6
Recurring | Short-term investments trading at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 35.4 | 79.2
Recurring | Real estate fund |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 109.4 | 111.4
Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) |  | 0.0
Total | 1,563.5 | 2,033.5
Recurring | Level 1 | Derivatives at fair value | Foreign exchange contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value | 0.0 | 0.0
Recurring | Level 1 | Derivatives at fair value | Interest rate swap |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value |  | 0.0
Recurring | Level 1 | Liabilities under derivative 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
Recurring | Level 1 | Total fixed income securities — Available for sale | Non-agency commercial mortgage-backed securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 |
Recurring | Level 1 | Fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 1,285.4 | 1,612.9
Recurring | Level 1 | Short-term investments |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 81.0 | 108.1
Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 161.7 | 233.3
Privately-held Investments, at fair value | 0.0 | 0.0
Catastrophe Bonds, Fair Value Disclosure | 0.0 | 0.0
Recurring | Level 1 | Short-term investments trading at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 35.4 | 79.2
Recurring | Level 1 | Real estate fund |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) |  | 0.0
Total | 3,795.4 | 4,204.6
Recurring | Level 2 | Derivatives at fair value | Foreign exchange contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value | 26.8 | 12.9
Recurring | Level 2 | Derivatives at fair value | Interest rate swap |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value |  | (78.3)
Recurring | Level 2 | Liabilities under derivative contracts | Foreign exchange contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Liabilities under derivative contracts, fair value | (13.6) | (8.9)
Recurring | Level 2 | Total fixed income securities — Available for sale | Non-agency commercial mortgage-backed securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 2.3 |
Recurring | Level 2 | Fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 3,062.7 | 3,345.3
Recurring | Level 2 | Short-term investments |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 6.8 | 9.5
Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 693.9 | 895.5
Privately-held Investments, at fair value | 0.0 | 0.0
Catastrophe Bonds, Fair Value Disclosure | 18.8 | 28.6
Recurring | Level 2 | Short-term investments trading at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Recurring | Level 2 | Real estate fund |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Recurring | Level 3 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) |  | 0.0
Total | 299.3 | 279.7
Recurring | Level 3 | Derivatives at fair value | Foreign exchange contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value | 0.0 | 0.0
Recurring | Level 3 | Derivatives at fair value | Interest rate swap |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Derivatives at fair value |  | 0.0
Recurring | Level 3 | Liabilities under derivative 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
Recurring | Level 3 | Total fixed income securities — Available for sale | Non-agency commercial mortgage-backed securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 |
Recurring | Level 3 | Fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Recurring | Level 3 | Short-term investments |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Privately-held Investments, at fair value | 299.3 | 279.7
Catastrophe Bonds, Fair Value Disclosure | 0.0 | 0.0
Recurring | Level 3 | Short-term investments trading at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Recurring | Level 3 | Real estate fund |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
U.S. government | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 1,101.2 | 1,413.1
U.S. government | Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 120.5 | 185.0
U.S. government | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 1,101.2 | 1,413.1
U.S. government | Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 120.5 | 185.0
U.S. government | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
U.S. government | Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
U.S. government | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
U.S. government | Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
U.S. agency | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 34.3 | 39.6
U.S. agency | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
U.S. agency | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 34.3 | 39.6
U.S. agency | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Municipal | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 67.1 | 50.7
Municipal | Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 3.5 | 3.2
Municipal | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Municipal | Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Municipal | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 67.1 | 50.7
Municipal | Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 3.5 | 3.2
Municipal | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Municipal | Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Corporate | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 273.1 | 1,959.8
Corporate | Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 103.5 | 243.2
Corporate | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 184.2 | 0.0
Corporate | Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Corporate | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 88.9 | 1,959.8
Corporate | Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 103.5 | 243.2
Corporate | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Corporate | Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Non-U.S. government-backed corporate | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 63.4 | 86.5
Non-U.S. government-backed corporate | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Non-U.S. government-backed corporate | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 63.4 | 86.5
Non-U.S. government-backed corporate | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Non-U.S government | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 7.4 | 328.8
Non-U.S government | Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 41.6 | 151.2
Non-U.S government | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 199.8
Non-U.S government | Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 41.2 | 48.3
Non-U.S government | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 7.4 | 129.0
Non-U.S government | Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.4 | 102.9
Non-U.S government | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Non-U.S government | Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Asset-backed | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 973.1 | 0.2
Asset-backed | Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 539.1 | 492.4
Asset-backed | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Asset-backed | Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Asset-backed | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 973.1 | 0.2
Asset-backed | Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 539.1 | 492.4
Asset-backed | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Asset-backed | Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Non-agency commercial mortgage-backed securities | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value |  | 6.5
Non-agency commercial mortgage-backed securities | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value |  | 0.0
Non-agency commercial mortgage-backed securities | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value |  | 6.5
Non-agency commercial mortgage-backed securities | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value |  | 0.0
Agency mortgage-backed | Recurring | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 1,826.2 | 1,073.0
Agency mortgage-backed | Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 37.6 | 53.8
Agency mortgage-backed | Recurring | Level 1 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Agency mortgage-backed | Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Agency mortgage-backed | Recurring | Level 2 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 1,826.2 | 1,073.0
Agency mortgage-backed | Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 37.6 | 53.8
Agency mortgage-backed | Recurring | Level 3 | Total fixed income securities — Available for sale |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | 0.0
Agency mortgage-backed | Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 | $ 0.0
High yield loans | Recurring | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 9.8 |
High yield loans | Recurring | Level 1 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 0.0 |
High yield loans | Recurring | Level 2 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | 9.8 |
High yield loans | Recurring | Level 3 | Held for trading financial assets, at fair value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments, fair value | $ 0.0 |

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- Definition Catastrophe Bonds, Fair Value Disclosure + References No definition available. + Details
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- Definition Debt Instrument, Accrued Interest and Payables, Fair Value Disclosure + References No definition available. + Details
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Namespace Prefix: | ahl_
Data Type: | xbrli:monetaryItemType
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- Definition Privately-held Investments, at fair value + References No definition available. + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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