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Fair Value Measurement - Narrative (Details) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2022 USD ($) Trust Security | Dec. 31, 2021
Assured IM |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Obligation to purchase debt | 0.05 |
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 | 190 |
Fixed maturity securities | $ 1,100 |
Recurring | Level 3 | CDR | Total | Minimum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 0.45% | 0.11%
Recurring | Level 3 | CDR | Total | Maximum |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |
Conditional prepayment rate | 2.93% | 1.78%

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- Definition Estimated rate of prepayment of principal on financial assets for initial fair value measurement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719 + Details
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