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Fair Value Measurement - Narrative (Details) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2023 USD ($) Security Trust | Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Repurchase agreement liability |  | $ 35
Assured IM |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Obligation to purchase debt |  | 0.05
Total |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Percentage of CDS contracts fair valued Using minimum premium | 11.20% |
AGC And AGM |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Number of custodial trusts | Trust | 4 |
Share value, amount | $ 200 |
Maximum amount | $ 50 |
Recurring | Level 3 |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Number of fixed maturity securities valued using model processes | Security | 189 |
Recurring | Level 3 | CDR | Total | Minimum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 3.62% | 2.78%
Recurring | Level 3 | CDR | Total | Maximum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 5.41% | 5.08%

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- Definition Amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(m)(1)(i)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(m)(1)(ii)(A)(ii)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1 + Details
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