v3.25.2
Fair value - Summary of Fair Value Assets Measured on Recurring Basis, Significant Unobservable Input (Details)
$ in Thousands
Jun. 30, 2025
USD ($)
Dec. 31, 2024
USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 5,896,818 $ 5,624,773
U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 2,851,475 2,825,679
Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 783,184 772,624
Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 261,415 8,364
Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 48,809  
Fair value, recurring    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 5,896,818 5,624,773
Fair value, recurring | U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 2,851,475 2,825,679
Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 783,184 772,624
Fair value, recurring | Residential mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 261,415 8,364
Fair value, recurring | Commercial mortgage-backed    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 48,809  
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) 0.0156  
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) 0.0094  
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) 0.0082  
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) 0.0126  
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) 0.0103  
Level 3  | Fair value, recurring    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value $ 256,110 281,541
Level 3  | Fair value, recurring | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 241,900  
Level 3  | Fair value, recurring | U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 206,717 222,786
Level 3  | Fair value, recurring | U.S. corporate | Internal models    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 206,717  
Level 3  | Fair value, recurring | Non-U.S. corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair value 46,103 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 35,164  
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