Insurance Contracts - Premium Earned (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Insurance [Line Items]
Premiums Earned, Net	$ 18	$ 11	$ 47	$ 39
Direct Premiums Written	65	16	181	83
Direct Premiums Earned	59	30	157	83
Assumed Reinsurance Premiums Written	14	0	14	0
Assumed Reinsurance Premiums Earned	3	0	3	0
Ceded Premiums Written	52	17	195	63
Ceded Reinsurance Premiums Earned	45	19	113	43
Premiums Written, Net	27	0	0	21
Premiums Receivable, Net	$ 278		$ 278		$ 269
Estimated Future Premium Payments Weighted Average Discounted Rate	3.20%		3.20%		3.00%
Weighted average period of future premiums			7 years 9 months 18 days		8 years
Reportable Geographical Components [Member] \| United States [Member]
Insurance [Line Items]
Premiums Earned, Net	$ 15	7	$ 38	27
Reportable Geographical Components [Member] \| United Kingdom [Member]
Insurance [Line Items]
Premiums Earned, Net	3	3	8	10
Reportable Geographical Components [Member] \| Other International [Member]
Insurance [Line Items]
Premiums Earned, Net	$ 0	$ 1	$ 2	$ 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.

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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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