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Reinsurance - Coverage and retention (Details) - Variable Interest Entity, Not Primary Beneficiary $ in Millions | 12 Months Ended
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Dec. 31, 2024 USD ($)
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | $ 1,720 |
Current Coverage | 1,409 |
Remaining Retention, Net | $ 818 |
Amortization period | 10 years |
Bellemeade 2021-3 Ltd |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | $ 639 | [1]
Current Coverage | 461 | [1]
Remaining Retention, Net | 132 | [1]
Bellemeade 2021-3 Ltd | Funded By VIE |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 508 |
Bellemeade 2021-3 Ltd | Directly provided capacity |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 131 |
Bellemeade 2022-1 Ltd |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 317 | [2]
Current Coverage | 218 | [2]
Remaining Retention, Net | 140 | [2]
Bellemeade 2022-1 Ltd | Funded By VIE |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 284 |
Bellemeade 2022-1 Ltd | Directly provided capacity |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 33 |
Bellemeade 2022-2 Ltd |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 327 | [3]
Current Coverage | 293 | [3]
Remaining Retention, Net | 199 | [3]
Bellemeade 2022-2 Ltd | Funded By VIE |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 201 |
Bellemeade 2022-2 Ltd | Directly provided capacity |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 126 |
Bellemeade 2023-1 Ltd |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 233 | [4]
Current Coverage | 233 | [4]
Remaining Retention, Net | 175 | [4]
Bellemeade 2023-1 Ltd | Funded By VIE |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 186 |
Bellemeade 2023-1 Ltd | Directly provided capacity |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 47 |
Bellemeade 2024-1 Ltd |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 204 | [5]
Current Coverage | 204 | [5]
Remaining Retention, Net | 172 | [5]
Bellemeade 2024-1 Ltd | Funded By VIE |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | 163 |
Bellemeade 2024-1 Ltd | Directly provided capacity |  |
Variable Interest Entity [Line Items] |  |
Initial Coverage at Issuance | $ 41 |
[1] | Issued in September 2021, covering in-force policies issued between April 1, 2021 and June 30, 2021. $508 million was directly funded by Bellemeade Re 2021-3 Ltd. via insurance-linked notes, with an additional $131 million capacity provided directly to Arch MI U.S. by a separate panel of reinsurers
[2] | Issued in January 2022, covering in-force policies issued between July 1, 2021 and November 30, 2021. $284 million was directly funded by Bellemeade Re 2022-1 Ltd. via insurance-linked notes, with an additional $33 million capacity provided directly to Arch MI U.S. by a separate panel of reinsurers.
[3] | Issued in September 2022, covering in-force policies issued between November 1, 2021 and June 30, 2022. $201 million was directly funded by Bellemeade Re 2022-2 Ltd. via insurance-linked notes, with an additional $126 million capacity provided directly to Arch MI U.S. by a separate panel of reinsurers
[4] | Issued in October 2023, covering in-force policies issued between January 1, 2023 and September 30, 2023. $186 million was directly funded by Bellemeade Re 2023-1 Ltd. via insurance-linked notes, with an additional $47 million capacity provided directly to Arch MI U.S. by a separate panel of reinsurers
[5] | Issued in August 2024, covering in-force policies issued between September 1, 2023 and July 31, 2024. $163 million was directly funded by Bellemeade Re 2024-1 Ltd. via insurance-linked notes, with an additional $41 million capacity provided directly to Arch MI U.S. by a separate panel of reinsurers

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