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Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	8 years 10 months 24 days	8 years 4 months 24 days
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 3,759	$ 4,212
Net Fair Value Asset (Liability)	(26)	(29)
Public finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	997	1,025
Net Fair Value Asset (Liability)	(11)	(12)
Public finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,645	2,044
Net Fair Value Asset (Liability)	(14)	(15)
Structured finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	143	150
Net Fair Value Asset (Liability)	(2)	(2)
Structured finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	974	993
Net Fair Value Asset (Liability)	$ 1	$ 0

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- References

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Represents the outstanding principal amounts of the underlying insured obligations that are accounted for as credit derivatives, net of protection purchased.

+ References

No definition available.

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- Definition

Average period covered by credit risk derivative contracts, 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/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
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-Section 50
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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.

+ References

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Fair value of credit risk derivative asset after deduction of credit risk derivative liability.

+ References

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