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Fair Value Measurements - Pricing Sources Used in Pricing Fixed Income Investments (Details) | Sep. 30, 2018 | Dec. 31, 2017
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Fair Value Disclosures [Abstract] |  |
Index providers | 85.00% | 84.00%
Pricing services | 13.00% | 11.00%
Broker-dealers | 2.00% | 5.00%
Total | 100.00% | 100.00%

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- Definition Fixed income investments brokers dealers. + References No definition available. + Details
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Namespace Prefix: | ahl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Fixed income investments index providers. + References No definition available. + Details
Name: | ahl_FixedIncomeInvestmentsIndexProviders
Namespace Prefix: | ahl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Fixed income investments pricing services. + References No definition available. + Details
Name: | ahl_FixedIncomeInvestmentsPricingServices
Namespace Prefix: | ahl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Total pricing sources used in pricing fixed income investments. + References No definition available. + Details
Name: | ahl_PricingSourcesUsedInPricingFixedIncomeInvestments
Namespace Prefix: | ahl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration