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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Investments, Authorized Amount To Invest

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Number of Outside Managers Managing Investment Portfolio

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- Definition

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 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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- Definition

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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- Definition

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

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No definition available.

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Amount of cash inflow from sale 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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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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No definition available.

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Investments - Additional Information (Details)	3 Months Ended		9 Months Ended
Investments - Additional Information (Details)	Sep. 30, 2021 USD ($) Security	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Security manager	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Security
Schedule of Investments [Line Items]
Number of outside managers managing investment portfolio \| manager			3
Accrued investment income	$ 79,000,000		$ 79,000,000		$ 75,000,000
Number of securities with unrealized losses greater than 10% of book value for 12 months or more \| Security	20		20		11
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more	$ 5,000,000		$ 5,000,000		$ 8,000,000
Assets held-in-trust	254,000,000		254,000,000		262,000,000
Proceeds from sale of fixed-maturity securities available-for-sale	0	$ 137,000,000	222,000,000	$ 627,000,000
PCD Accounting Model to PCI Securities
Schedule of Investments [Line Items]
Additional credit loss expense	4,000,000		1,000,000	$ 14,000,000
AGL Subsidiaries
Schedule of Investments [Line Items]
Assets held-in-trust	1,236,000,000		1,236,000,000		1,511,000,000
Fair Value Measured at Net Asset Value Per Share \| Healthcare Private Equity Fund
Schedule of Investments [Line Items]
Long-term purchase commitment, amount			121,000,000
Future Equity Investments
Schedule of Investments [Line Items]
Remaining minimum amount committed	209,000,000		209,000,000
Future Equity Investments \| AssuredIM managed fixed-maturity securities \| AGL Subsidiaries
Schedule of Investments [Line Items]
Investments, authorized amount to invest	750,000,000		750,000,000
Invested Capital \| AssuredIM managed fixed-maturity securities \| AGL Subsidiaries
Schedule of Investments [Line Items]
Long-term purchase commitment, amount			380,000,000
Unfunded Commitment \| AssuredIM managed fixed-maturity securities \| AGL Subsidiaries
Schedule of Investments [Line Items]
Long-term purchase commitment, amount			279,000,000
Equity Method Investments \| AssuredIM managed fixed-maturity securities \| AGL Subsidiaries
Schedule of Investments [Line Items]
Long-term purchase commitment, amount			659,000,000
Equity Method Investments \| AssuredIM managed fixed-maturity securities \| AGAS
Schedule of Investments [Line Items]
Investments, fair value disclosure	$ 465,000,000		$ 465,000,000		$ 345,000,000