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Investments - Additional Information (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2022 USD ($) Security | Jun. 30, 2022 USD ($) Security manager | Jun. 30, 2021 USD ($) | Dec. 31, 2021 USD ($) Security
Schedule of Investments [Line Items] |  |  |  |
Number of outside managers managing investment portfolio | manager |  | 3 |  |
Accrued investment income | $ 74 | $ 74 |  | $ 69
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | Security | 435 | 435 |  | 23
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more | $ 211 | $ 211 |  | $ 6
Assets held-in-trust | 217 | 217 |  | 243
PCD Accounting Model to PCI Securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Allowance for credit loss | 4 | 9 | $ 3 |
AGL Subsidiaries |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Assets held-in-trust | 1,149 | 1,149 |  | 1,231
Future Equity Investments |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Remaining minimum amount committed | 96 | 96 |  |
Future Equity Investments | AGL Subsidiaries | AssuredIM managed fixed-maturity securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Investments, authorized amount to invest | 750 | 750 |  |
Investments, including distributed gains, authorized amount to invest | 810 | 810 |  |
Invested Capital | AGL Subsidiaries | AssuredIM managed fixed-maturity securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Long-term purchase commitment, amount |  | 516 |  |
Unfunded Commitment | AGL Subsidiaries | AssuredIM managed fixed-maturity securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Long-term purchase commitment, amount |  | 241 |  |
Equity in Earnings (Losses) of Investees | AGL Subsidiaries | AssuredIM managed fixed-maturity securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Long-term purchase commitment, amount |  | 757 |  |
Equity in Earnings (Losses) of Investees | AGAS | AssuredIM managed fixed-maturity securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Investments, fair value disclosure | $ 549 | $ 549 |  | $ 543

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- Definition This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for those securities which are categorized neither as held-to-maturity nor trading securities and which have unrealized losses greater than 10% of book value. + References No definition available. + Details
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