Investments and Cash - Narrative (Details) $ in Millions		12 Months Ended
	Jul. 01, 2023 USD ($)	Dec. 31, 2023 USD ($) Security fund manager	Dec. 31, 2022 USD ($) Security	Dec. 31, 2021 USD ($)
Schedule of Cost-method Investments [Line Items]
Number of investment portfolio managers | manager		3
Accounted for as consolidated investment vehicles | fund		3
Total number of investments | fund		8
Investments, fair value	$ 450
Accrued investment income		$ 71	$ 71
Number of securities with unrealized losses greater than 10% of book value for 12 months or more | Security		409	567
Total unrealized losses for securities having losses greater than 10% of book value for 12 months or more		$ 200	$ 329
Assets held-in-trust		234	222
Non-income producing investments		0	0
Purchased with credit deterioration, amount at purchase price			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
Other invested assets (includes $3 and $30, at fair value)		829	133
Indefinite-lived intangible assets		6	6
Finite-lived intangible assets		0	40
Nonconsolidated Investees, Other
Schedule of Cost-method Investments [Line Items]
Investments, fair value	25
Sound Point
Schedule of Cost-method Investments [Line Items]
Investments, fair value	$ 425	631
Useful life	6 years 4 months 24 days
Disposal Group, Held-for-Sale, Not Discontinued Operations | Sound Point Agreement
Schedule of Cost-method Investments [Line Items]
Investment management commitment	$ 1,000	1,000
Assured Guaranty Subsidiaries
Schedule of Cost-method Investments [Line Items]
Assets held-in-trust		1,154	1,169
AssuredIM Funds | Equity in Earnings (Losses) of Investees | Assured Guaranty Asset Strategies LLC
Schedule of Cost-method Investments [Line Items]
Fair value of investment		571
Equity Securities
Schedule of Cost-method Investments [Line Items]
Cash dividends from subsidiaries		7	10	$ 15
Alternative Investment | Equity in Earnings (Losses) of Investees | Assured Guaranty Asset Strategies LLC
Schedule of Cost-method Investments [Line Items]
Long-term purchase commitment, amount		775
Investments, funded amount		534
Alternative Investment | Future Equity Investments
Schedule of Cost-method Investments [Line Items]
Authorized amount to invest		1,500
Fair value of investment		739
Unfunded committment		779
Committed for specific funds		363
Investments, including distributed gains, authorized amount to invest		108
Alternative Investment | Future Equity Investments | Assured Guaranty Subsidiaries
Schedule of Cost-method Investments [Line Items]
Authorized amount to invest		858
Authorized amount to invest, excluding distributed gains		750
Sound Point
Schedule of Cost-method Investments [Line Items]
Other invested assets (includes $3 and $30, at fair value)		429	$ 0
Indefinite-lived intangible assets		243
Finite-lived intangible assets		$ 37