XML 107 R88.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Reserves for Losses and Adjustment Expenses Short-duration Insurance Contracts, Claims by Accident Year (Details) $ in Millions | Dec. 31, 2018 USD ($) Integer | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($)
--- | --- | --- | --- | --- | --- | --- | ---
Claims Development [Line Items] |  |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | $ 4,944.4 |  |  |  |  |  |
Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,296.6 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 1,046.3 |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 250.3 |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 3.1 |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 253.4 |  |  |  |  |  |
Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 983.2 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 361.0 |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 622.2 |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 43.3 |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 665.5 |  |  |  |  |  |
Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,855.8 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 1,263.1 |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 592.7 |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 29.1 |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 621.8 |  |  |  |  |  |
Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,064.0 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 502.8 |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 561.2 |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 20.0 |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 581.2 |  |  |  |  |  |
Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,903.9 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 1,381.3 |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 522.6 |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 20.0 |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 542.6 |  |  |  |  |  |
Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,572.6 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 501.6 |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 1,071.0 |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 485.1 |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 1,556.1 |  |  |  |  |  |
Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 1,602.0 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | 919.7 |  |  |  |  |  |
All outstanding liabilities for 2012 and subsequent years, net of reinsurance | 682.3 |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 41.5 |  |  |  |  |  |
Liability for claims and claim adjustment expenses, net of reinsurance | 723.8 |  |  |  |  |  |
Accident Year 2012 | Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 151.9 | $ 152.9 | $ 158.8 | $ 164.4 | $ 165.6 | $ 166.8 | $ 168.5
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 0.0 |  |  |  |  |  |
Number of Reported Claims | Integer | 6,141 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 152.5 | 153.1 | 155.7 | 151.7 | 137.9 | 128.5 | 41.1
Accident Year 2012 | Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 67.6 | 65.7 | 68.0 | 60.1 | 69.0 | 61.8 | 77.1
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 7.9 |  |  |  |  |  |
Number of Reported Claims | Integer | 2,869 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 49.3 | 48.5 | 40.2 | 29.3 | 13.9 | 6.5 | 1.3
Accident Year 2012 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 316.1 | 327.8 | 331.6 | 346.1 | 325.5 | 306.0 | 268.5
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 2.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 3,807 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 273.3 | 250.5 | 239.6 | 210.9 | 174.6 | 132.2 | 51.5
Accident Year 2012 | Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 99.8 | 88.4 | 92.8 | 95.8 | 92.6 | 89.0 | 87.5
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 6.6 |  |  |  |  |  |
Number of Reported Claims | Integer | 573 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 79.0 | 69.7 | 64.5 | 58.7 | 50.3 | 39.4 | 22.8
Accident Year 2012 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 271.9 | 279.5 | 282.5 | 279.1 | 286.6 | 303.4 | 280.1
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 11.2 |  |  |  |  |  |
Number of Reported Claims | Integer | 669 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 232.3 | 227.8 | 216.7 | 209.1 | 188.9 | 135.8 | 35.6
Accident Year 2012 | Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 240.7 | 231.7 | 230.6 | 233.5 | 242.2 | 231.1 | 232.9
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 42.9 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,735 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 133.6 | 116.9 | 95.7 | 65.1 | 41.7 | 17.5 | 2.2
Accident Year 2012 | Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 169.9 | 173.5 | 172.9 | 174.6 | 188.9 | 199.7 | 176.4
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 8.4 |  |  |  |  |  |
Number of Reported Claims | Integer | 628 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 151.1 | 149.8 | 144.5 | 139.1 | 129.0 | 93.9 | $ 25.1
Accident Year 2013 | Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 110.6 | 112.5 | 111.5 | 115.8 | 116.1 | 128.7 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 0.6 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,992 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 107.4 | 104.6 | 100.1 | 88.2 | 75.0 | 38.3 |
Accident Year 2013 | Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 103.2 | 102.0 | 119.0 | 113.6 | 115.0 | 131.2 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 11.6 |  |  |  |  |  |
Number of Reported Claims | Integer | 3,161 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 79.7 | 67.4 | 52.3 | 39.0 | 25.5 | 2.2 |
Accident Year 2013 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 346.2 | 332.6 | 325.5 | 342.0 | 333.4 | 320.6 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 6.0 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,171 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 284.1 | 264.4 | 235.0 | 204.7 | 131.4 | 41.5 |
Accident Year 2013 | Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 90.8 | 99.7 | 100.7 | 104.0 | 99.8 | 105.2 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 12.0 |  |  |  |  |  |
Number of Reported Claims | Integer | 571 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 72.0 | 63.6 | 65.3 | 31.1 | 21.0 | 8.0 |
Accident Year 2013 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 172.9 | 176.2 | 177.7 | 188.9 | 198.8 | 216.8 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 2.1 |  |  |  |  |  |
Number of Reported Claims | Integer | 806 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 164.2 | 162.6 | 158.0 | 146.0 | 98.0 | 34.4 |
Accident Year 2013 | Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 199.9 | 204.7 | 221.7 | 224.3 | 229.0 | 213.8 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 44.8 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,605 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 114.3 | 92.4 | 64.7 | 42.5 | 15.8 | 3.4 |
Accident Year 2013 | Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 115.6 | 119.5 | 120.2 | 131.9 | 139.8 | 144.6 |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 5.5 |  |  |  |  |  |
Number of Reported Claims | Integer | 568 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 101.6 | 101.6 | 94.6 | 87.3 | 71.3 | $ 25.1 |
Accident Year 2014 | Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 133.4 | 134.2 | 133.5 | 156.3 | 164.3 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 1.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 8,740 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 127.1 | 123.1 | 113.5 | 86.1 | 40.2 |  |
Accident Year 2014 | Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 134.3 | 127.2 | 137.2 | 125.4 | 142.9 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 23.4 |  |  |  |  |  |
Number of Reported Claims | Integer | 3,628 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 71.9 | 58.8 | 32.2 | 13.1 | 2.6 |  |
Accident Year 2014 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 305.8 | 310.3 | 298.7 | 313.8 | 309.6 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 9.5 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,001 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 232.4 | 209.7 | 189.1 | 116.6 | 53.4 |  |
Accident Year 2014 | Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 130.5 | 119.3 | 129.0 | 130.3 | 134.5 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 17.3 |  |  |  |  |  |
Number of Reported Claims | Integer | 795 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 86.3 | 72.0 | 53.4 | 30.6 | 2.9 |  |
Accident Year 2014 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 150.7 | 150.4 | 161.7 | 177.5 | 190.2 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 4.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 863 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 141.6 | 137.7 | 127.6 | 101.0 | 37.6 |  |
Accident Year 2014 | Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 202.5 | 209.1 | 215.8 | 207.3 | 204.4 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 56.1 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,636 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 86.3 | 60.2 | 37.8 | 13.8 | 2.5 |  |
Accident Year 2014 | Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 126.4 | 123.6 | 132.6 | 140.7 | 152.4 |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 10.9 |  |  |  |  |  |
Number of Reported Claims | Integer | 610 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 100.1 | 89.6 | 81.6 | 56.7 | $ 16.6 |  |
Accident Year 2015 | Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 200.0 | 197.7 | 203.0 | 237.4 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 9.1 |  |  |  |  |  |
Number of Reported Claims | Integer | 10,319 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 177.5 | 168.4 | 141.0 | 56.9 |  |  |
Accident Year 2015 | Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 201.6 | 184.1 | 221.5 | 201.5 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 33.6 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,463 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 91.8 | 56.0 | 16.8 | 3.1 |  |  |
Accident Year 2015 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 285.8 | 281.9 | 299.8 | 297.1 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 17.6 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,001 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 193.7 | 174.0 | 123.3 | 44.9 |  |  |
Accident Year 2015 | Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 189.0 | 184.9 | 174.9 | 173.5 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 60.3 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,080 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 89.2 | 69.9 | 43.4 | 13.7 |  |  |
Accident Year 2015 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 156.9 | 177.6 | 187.8 | 214.9 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 4.6 |  |  |  |  |  |
Number of Reported Claims | Integer | 991 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 139.4 | 126.6 | 95.2 | 35.9 |  |  |
Accident Year 2015 | Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 212.8 | 210.4 | 200.9 | 193.8 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 74.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,664 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 65.5 | 38.4 | 18.0 | 3.5 |  |  |
Accident Year 2015 | Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 159.8 | 165.4 | 170.9 | 166.9 |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 18.8 |  |  |  |  |  |
Number of Reported Claims | Integer | 761 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 122.6 | 104.6 | 56.8 | $ 17.7 |  |  |
Accident Year 2016 | Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 242.6 | 247.7 | 236.7 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 12.4 |  |  |  |  |  |
Number of Reported Claims | Integer | 9,431 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 200.2 | 167.8 | 66.5 |  |  |  |
Accident Year 2016 | Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 181.6 | 186.3 | 215.3 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 81.8 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,388 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 39.6 | 22.5 | 4.1 |  |  |  |
Accident Year 2016 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 229.6 | 230.5 | 260.9 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 32.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,373 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 142.8 | 82.6 | 30.9 |  |  |  |
Accident Year 2016 | Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 215.6 | 211.1 | 190.3 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 83.4 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,303 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 94.9 | 71.2 | 15.2 |  |  |  |
Accident Year 2016 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 268.2 | 269.8 | 269.9 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 23.2 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,211 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 204.3 | 163.3 | 56.3 |  |  |  |
Accident Year 2016 | Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 244.9 | 245.2 | 232.6 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 115.0 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,416 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 63.9 | 33.5 | 9.1 |  |  |  |
Accident Year 2016 | Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 238.7 | 240.7 | 239.8 |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 37.9 |  |  |  |  |  |
Number of Reported Claims | Integer | 902 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 166.2 | 151.4 | $ 58.9 |  |  |  |
Accident Year 2017 | Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 257.0 | 293.9 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 23.6 |  |  |  |  |  |
Number of Reported Claims | Integer | 7,722 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 212.3 | 96.0 |  |  |  |  |
Accident Year 2017 | Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 173.1 | 179.6 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 82.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,815 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 24.7 | 3.5 |  |  |  |  |
Accident Year 2017 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 200.9 | 210.6 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 44.5 |  |  |  |  |  |
Number of Reported Claims | Integer | 5,939 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 108.1 | 40.2 |  |  |  |  |
Accident Year 2017 | Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 181.9 | 205.9 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 102.1 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,760 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 57.6 | 27.1 |  |  |  |  |
Accident Year 2017 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 534.8 | 557.8 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 47.5 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,846 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 374.7 | 123.4 |  |  |  |  |
Accident Year 2017 | Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 242.7 | 244.7 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 158.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,085 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 30.8 | 8.9 |  |  |  |  |
Accident Year 2017 | Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 393.0 | 380.5 |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 81.1 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,191 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 250.2 | $ 95.0 |  |  |  |  |
Accident Year 2018 | Property Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 201.1 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 31.4 |  |  |  |  |  |
Number of Reported Claims | Integer | 5,694 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 69.3 |  |  |  |  |  |
Accident Year 2018 | Casualty Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 121.8 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 103.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 3,918 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 4.0 |  |  |  |  |  |
Accident Year 2018 | Marine, Aviation and Energy Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 171.4 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 85.3 |  |  |  |  |  |
Number of Reported Claims | Integer | 3,212 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 28.7 |  |  |  |  |  |
Accident Year 2018 | Financial and Professional Insurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 156.4 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 124.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 4,221 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 23.8 |  |  |  |  |  |
Accident Year 2018 | Property Catastrophe and Other Property Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 348.5 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 182.8 |  |  |  |  |  |
Number of Reported Claims | Integer | 1,182 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 124.8 |  |  |  |  |  |
Accident Year 2018 | Casualty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 229.1 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 195.4 |  |  |  |  |  |
Number of Reported Claims | Integer | 481 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 7.2 |  |  |  |  |  |
Accident Year 2018 | Specialty Reinsurance |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |
Incurred Claims and Allocated Claim Adjustment Expense, Net | 398.6 |  |  |  |  |  |
Incurred but Not Reported (IBNR) Claims Liability, Net | $ 327.7 |  |  |  |  |  |
Number of Reported Claims | Integer | 914 |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, Net | $ 27.9 |  |  |  |  |  |

X
- Definition Undiscounted subtotal amount, after reinsurance, of the liability for unpaid claim adjustment expense for short durations insurance contracts not separately presented in claim development information. + References No definition available. + Details
Name: | ahl_ShortDurationInsuranceContractsLiabilityforUnpaidClaimAdjustmentExpenseNetNotSeparatelyPresentedSubtotal
Namespace Prefix: | ahl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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_ClaimsDevelopmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after reinsurance, of paid claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671311-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsCumulativePaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of incurred-but-not-reported (IBNR) liabilities plus expected development on reported claims, for claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4E -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671321-158438 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4D -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671317-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsIncurredButNotReportedIbnrClaimsLiabilityNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of incurred claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671311-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsIncurredClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4C -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671315-158438 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671311-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts for accident years not separately presented in claim development information. Excludes unallocated claim adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671311-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNetNotSeparatelyPresented
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Cumulative number of reported claims for short-duration insurance contracts. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4D -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99384497&loc=SL65671317-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsNumberOfReportedClaims
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_PropertyInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=ahl_CasualtyCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=ahl_MarineAviationandEnergyCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=ahl_FinancialandProfessionalCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=ahl_AssumedPropertyCatastropheandOtherPropertyCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=ahl_AssumedCasualtyCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=ahl_AssumedSpecialtyCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2012Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2013Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2014Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2015Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2016Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractsAccidentYear2017Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractsAccidentYear2018Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |