XML 57 R46.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Investments - Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Trading Investments in Fixed Income Maturities (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Statement [Line Items] |  |
Fair Market Value | $ 1,637.6 | $ 1,649.3
U.S. government |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 141.8 | 162.3
Gross Unrealized Gains | 0.6 | 0.4
Gross Unrealized Losses | (0.7) | (0.8)
Fair Market Value | 141.7 | 161.9
Municipal |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 75.0 | 32.4
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | (0.7) | (0.2)
Fair Market Value | 74.3 | 32.2
Corporate |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 1,014.5 | 1,036.5
Gross Unrealized Gains | 5.8 | 14.0
Gross Unrealized Losses | (16.7) | (4.2)
Fair Market Value | 1,003.6 | 1,046.3
Non-U.S. government-backed corporate |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 1.0 | 1.0
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | 0.0 | 0.0
Fair Market Value | 1.0 | 1.0
Non-U.S. government |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 216.2 | 196.1
Gross Unrealized Gains | 3.4 | 6.9
Gross Unrealized Losses | (3.0) | (0.5)
Fair Market Value | 216.6 | 202.5
Asset-backed |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 8.4 | 9.9
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | (0.1) | 0.0
Fair Market Value | 8.3 | 9.9
Agency mortgage-backed |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 195.8 | 196.7
Gross Unrealized Gains | 0.3 | 0.2
Gross Unrealized Losses | (4.0) | (1.4)
Fair Market Value | 192.1 | 195.5
Total fixed income securities — Trading |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 1,652.7 | 1,634.9
Gross Unrealized Gains | 10.1 | 21.5
Gross Unrealized Losses | (25.2) | (7.1)
Fair Market Value | 1,637.6 | 1,649.3
Total short-term investments — Trading |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 27.0 | 73.0
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | 0.0 | 0.0
Fair Market Value | 27.0 | 73.0
Total equity securities — Trading |  |
Statement [Line Items] |  |
Cost or Amortized Cost |  | 414.8
Gross Unrealized Gains |  | 83.5
Gross Unrealized Losses |  | (7.3)
Fair Market Value |  | 491.0
Total catastrophe bonds — Trading |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 35.0 | 33.5
Gross Unrealized Gains | 0.0 | 0.0
Gross Unrealized Losses | (0.2) | (1.1)
Fair Market Value | 34.8 | 32.4
Total |  |
Statement [Line Items] |  |
Cost or Amortized Cost | 1,714.7 | 2,156.2
Gross Unrealized Gains | 10.1 | 105.0
Gross Unrealized Losses | (25.4) | (15.5)
Fair Market Value | $ 1,699.4 | $ 2,245.7

X
- Definition Trading Securities, Accumulated Gross Unrealized Gain, before Tax + References No definition available. + Details
Name: | ahl_TradingSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
Namespace Prefix: | ahl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Trading Securities, Accumulated Gross Unrealized Loss, before Tax + References No definition available. + Details
Name: | ahl_TradingSecuritiesAccumulatedGrossUnrealizedLossbeforeTax
Namespace Prefix: | ahl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Trading Securities, Amortized Cost Basis + References No definition available. + Details
Name: | ahl_TradingSecuritiesAmortizedCostBasis
Namespace Prefix: | ahl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 + Details
Name: | us-gaap_TradingSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MunicipalBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ForeignCorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=ahl_TradingFixedMaturityInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=ahl_CatastropheBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=ahl_TotalTradingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |