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Reinsurance and Indemnification - 2018-1 Excess Catastrophe Reinsurance Contract (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Mar. 31, 2019 | Dec. 31, 2018
Reinsurance Retention Policy [Line Items] |  |  |
Retention amount for catastrophe reinsurance agreement contracts |  |  | $ 500
2018-1 Excess Catastrophe Reinsurance Contract |  |  |
Reinsurance Retention Policy [Line Items] |  |  |
Retention percentage of reinsurance limit |  |  | 100.00%
Limit of aggregate losses under aggregate excess agreement | $ 500 |  | $ 500
Term of catastrophe reinsurance agreement contract |  |  | 4 years
Losses in multiple exposures, retention amount annual limit |  |  | $ 1
Minimum | 2018-1 Excess Catastrophe Reinsurance Contract |  |  |
Reinsurance Retention Policy [Line Items] |  |  |
Retention amount for catastrophe reinsurance agreement contracts |  |  | 3,750
Retention amount annual limit |  |  | 3,750
Maximum | 2018-1 Excess Catastrophe Reinsurance Contract |  |  |
Reinsurance Retention Policy [Line Items] |  |  |
Retention amount for catastrophe reinsurance agreement contracts |  |  | $ 4,250
Scenario, Forecast | 2018-1 Excess Catastrophe Reinsurance Contract |  |  |
Reinsurance Retention Policy [Line Items] |  |  |
Retention percentage of reinsurance limit |  | 100.00% |
Limit of aggregate losses under aggregate excess agreement |  | $ 500 |
Scenario, Forecast | Minimum | 2018-1 Excess Catastrophe Reinsurance Contract |  |  |
Reinsurance Retention Policy [Line Items] |  |  |
Retention amount for catastrophe reinsurance agreement contracts |  | 4,000 |
Scenario, Forecast | Maximum | 2018-1 Excess Catastrophe Reinsurance Contract |  |  |
Reinsurance Retention Policy [Line Items] |  |  |
Retention amount for catastrophe reinsurance agreement contracts |  | $ 4,500 |

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- Definition Represents the retention percentage of annual coverage limit provided by the insurance arrangement for catastrophe claims. + References No definition available. + Details
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- Definition The limit of aggregated losses per contract year beyond which coverage provided by an aggregate excess agreement applies. + References No definition available. + Details
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- Definition Represents the period of catastrophe reinsurance agreement contract. + References No definition available. + Details
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- Definition Catastrophe Reinsurance Agreement Contracts, Losses In Multiple Exposures, Retention Amount Annual limit + References No definition available. + Details
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- Definition Represents the retention amount of catastrophe reinsurance agreement contracts. + References No definition available. + Details
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- Definition Catastrophe Reinsurance Agreement Contracts, Retention Amount Annual limit + References No definition available. + Details
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