Represents the number of securities which had unrealized losses greater than 10% of book value for 12 months or more.

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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.

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Number of Outside Managers Managing Investment Portfolio

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Interest, dividends, rents, ancillary and other revenues earned but not yet received by the entity on its investments.

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The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations.

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Amount, excluding accrued interest, of increase (decrease) in allowance for credit loss of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, excluding accrued interest, of allowance for credit loss at acquisition date of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) purchased with credit deterioration.

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Amount at par value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), purchased with credit deterioration.

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Amount at purchase price of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), purchased with credit deterioration.

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Amount of discount (premium) attributable to other factors on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), purchased with credit deterioration.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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The minimum amount the entity agreed to spend under the long-term purchase commitment.

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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Investments - Additional Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) Security	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) manager Security	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) Security
Schedule of Investments [Line Items]
Number of outside managers managing investment portfolio \| manager			3
Accrued investment income	$ 72		$ 72		$ 69
Number of securities with unrealized losses greater than 10% of book value for 12 months or more \| Security	687		687		23
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	$ 450		$ 450		$ 6
Assets held-in-trust	211		211		243
Allowance for credit loss	(4)	$ 5	(13)	$ 1
Securities purchased with credit deterioration	22
Securities purchased with credit deterioration, amount at par value	31
Allowance for credit loss at acquisition date	2
Discount attributable to other factors	7
PCD Accounting Model to PCI Securities
Schedule of Investments [Line Items]
Allowance for credit loss	4	$ (4)	13	$ (1)
AGL Subsidiaries
Schedule of Investments [Line Items]
Assets held-in-trust	1,174		1,174		1,231
Future Equity Investments
Schedule of Investments [Line Items]
Remaining minimum amount committed	92		92
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			536
Unfunded Commitment \| AGL Subsidiaries \| AssuredIM managed fixed-maturity securities
Schedule of Investments [Line Items]
Long-term purchase commitment, amount			219
Equity in Earnings (Losses) of Investees \| AGL Subsidiaries \| AssuredIM managed fixed-maturity securities
Schedule of Investments [Line Items]
Long-term purchase commitment, amount			755
Equity in Earnings (Losses) of Investees \| AGAS \| AssuredIM managed fixed-maturity securities
Schedule of Investments [Line Items]
Investments, fair value disclosure	$ 574		$ 574		$ 543