Insurance Contracts - Premium Earned (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Insurance [Line Items]
Premiums Earned, Net	$ 33	$ 18	$ 99	$ 47
Direct Premiums Written	91	65	265	181
Direct Premiums Earned	89	59	243	157
Assumed Reinsurance Premiums Written	22	14	60	14
Assumed Reinsurance Premiums Earned	17	3	50	3
Ceded Premiums Written	83	52	232	195
Ceded Reinsurance Premiums Earned	73	45	194	113
Premiums Written, Net	31	27	92	0
Premiums Receivable, Net	$ 342		$ 342		$ 290
Estimated Future Premium Payments Weighted Average Discounted Rate	3.10%		3.10%		3.20%
Weighted average period of future premiums			7 years 4 months 24 days		8 years
Reportable Geographical Components [Member] \| United States [Member]
Insurance [Line Items]
Premiums Earned, Net	$ 30	15	$ 90	38
Reportable Geographical Components [Member] \| United Kingdom [Member]
Insurance [Line Items]
Premiums Earned, Net	3	3	8	8
Reportable Geographical Components [Member] \| Other International [Member]
Insurance [Line Items]
Premiums Earned, Net	$ 0	$ 0	$ 1	$ 2

Weighted average discounted rate of estimated future premium payments to be paid by the VIEs.

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Insurance [Line Items]

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Amount of earned premiums assumed from other entities.

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Amount of written premiums assumed from other entities.

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Amount of earned premiums ceded to other entities.

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Amount of written premiums ceded to other entities.

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Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums written.

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Weighted average period over which premium receivable for financial guarantee insurance contracts is collected where premium is received over the contract period, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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The carrying amount as of the balance sheet date due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, net of the allowance for doubtful accounts.

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Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums written.

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