Reinsurance - Schedule of Retained Aggregate Loss and Initial and Current Reinsurance Coverage (Details) $ in Millions	Jun. 30, 2026 USD ($)
Reinsurance Policy, Type [Axis]: 2021 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	$ 671
Current first layer retained loss	652
Initial reinsurance coverage	206
Current reinsurance coverage	38
Reinsurance Policy, Type [Axis]: 2022-1 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	462
Current first layer retained loss	422
Initial reinsurance coverage	196
Current reinsurance coverage	126
Reinsurance Policy, Type [Axis]: 2022-2 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	385
Current first layer retained loss	345
Initial reinsurance coverage	25
Current reinsurance coverage	25
Reinsurance Policy, Type [Axis]: 2022-3 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	317
Current first layer retained loss	305
Initial reinsurance coverage	289
Current reinsurance coverage	98
Reinsurance Policy, Type [Axis]: 2022-4 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	264
Current first layer retained loss	253
Initial reinsurance coverage	36
Current reinsurance coverage	36
Reinsurance Policy, Type [Axis]: 2022-5 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	256
Current first layer retained loss	234
Initial reinsurance coverage	201
Current reinsurance coverage	119
Reinsurance Policy, Type [Axis]: 2023-1 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	360
Current first layer retained loss	339
Initial reinsurance coverage	180
Current reinsurance coverage	128
Reinsurance Policy, Type [Axis]: 2024-1 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	362
Current first layer retained loss	356
Initial reinsurance coverage	270
Current reinsurance coverage	254
Reinsurance Policy, Type [Axis]: 2024-2 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	134
Current first layer retained loss	129
Initial reinsurance coverage	90
Current reinsurance coverage	60
Reinsurance Policy, Type [Axis]: 2025-1 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	354
Current first layer retained loss	353
Initial reinsurance coverage	180
Current reinsurance coverage	180
Reinsurance Policy, Type [Axis]: 2025-2 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	294
Current first layer retained loss	294
Initial reinsurance coverage	28
Current reinsurance coverage	28
Reinsurance Policy, Type [Axis]: 2026-1 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	194
Current first layer retained loss	194
Initial reinsurance coverage	94
Current reinsurance coverage	94
Reinsurance Policy, Type [Axis]: 2026-2 XOL
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	160
Current first layer retained loss	160
Initial reinsurance coverage	12
Current reinsurance coverage	12
Reinsurance Policy, Type [Axis]: Mortgage Insurance-Linked Notes
Reinsurance Retention Policy [Line Items]
Current reinsurance coverage	266
Reinsurance Policy, Type [Axis]: Traditional Excess-of-Loss Reinsurance
Reinsurance Retention Policy [Line Items]
Current reinsurance coverage	1,198
Reinsurance Policy, Type [Axis]: Triangle Re 2021-2 Ltd.
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	189
Current first layer retained loss	186
Initial reinsurance coverage	303
Current reinsurance coverage	44
Reinsurance Policy, Type [Axis]: Triangle Re 2021-3 Ltd.
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	304
Current first layer retained loss	297
Initial reinsurance coverage	372
Current reinsurance coverage	70
Reinsurance Policy, Type [Axis]: Triangle Re 2023-1 Ltd.
Reinsurance Retention Policy [Line Items]
Initial first layer retained loss	244
Current first layer retained loss	233
Initial reinsurance coverage	248
Current reinsurance coverage	$ 152