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Fair value - Summary of Fair Value Assets Measured on Recurring Basis, Significant Unobservable Input (Details) $ in Thousands | Mar. 31, 2025 USD ($) | Dec. 31, 2024 USD ($)
--- | --- | ---
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | $ 5,815,337 | $ 5,624,773
U.S. corporate |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 2,900,205 | 2,825,679
Non-U.S. corporate |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 768,953 | 772,624
Residential mortgage-backed |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 111,683 | 8,364
Commercial mortgage-backed |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 20,702 |
Fair value, recurring |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 5,815,337 | 5,624,773
Fair value, recurring | U.S. corporate |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 2,900,205 | 2,825,679
Fair value, recurring | Non-U.S. corporate |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 768,953 | 772,624
Fair value, recurring | Residential mortgage-backed |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 111,683 | 8,364
Fair value, recurring | Commercial mortgage-backed |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | $ 20,702 |
Level 3 | U.S. corporate | Internal models | Credit spreads | Minimum |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fixed maturity securities, measurement input (in basis points) | 0.0014 |
Level 3 | U.S. corporate | Internal models | Credit spreads | Maximum |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fixed maturity securities, measurement input (in basis points) | 0.0174 |
Level 3 | U.S. corporate | Internal models | Credit spreads | Weighted average |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fixed maturity securities, measurement input (in basis points) | 0.0102 |
Level 3 | Non-U.S. corporate | Internal models | Credit spreads | Minimum |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fixed maturity securities, measurement input (in basis points) | 0.0090 |
Level 3 | Non-U.S. corporate | Internal models | Credit spreads | Maximum |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fixed maturity securities, measurement input (in basis points) | 0.0143 |
Level 3 | Non-U.S. corporate | Internal models | Credit spreads | Weighted average |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fixed maturity securities, measurement input (in basis points) | 0.0118 |
Level 3 | Fair value, recurring |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | $ 279,704 | 281,541
Level 3 | Fair value, recurring | Internal models |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 264,600 |
Level 3 | Fair value, recurring | U.S. corporate |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 225,970 | 222,786
Level 3 | Fair value, recurring | U.S. corporate | Internal models |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 225,970 |
Level 3 | Fair value, recurring | Non-U.S. corporate |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 50,474 | 56,553
Level 3 | Fair value, recurring | Non-U.S. corporate | Internal models |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 38,603 |
Level 3 | Fair value, recurring | Residential mortgage-backed |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | 0 | $ 0
Level 3 | Fair value, recurring | Commercial mortgage-backed |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair value | $ 0 |

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