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Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024
Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	9 years 1 month 6 days	8 years 4 months 24 days
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 3,761	$ 4,212
Net Fair Value Asset (Liability)	(30)	(29)
Public finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,021	1,025
Net Fair Value Asset (Liability)	(12)	(12)
Public finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,627	2,044
Net Fair Value Asset (Liability)	(16)	(15)
Structured finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	148	150
Net Fair Value Asset (Liability)	(2)	(2)
Structured finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	965	993
Net Fair Value Asset (Liability)	$ 0	$ 0

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- References

No definition available.

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- Definition

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

+ References

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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://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4K
-Subparagraph (a)(1)
-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4K

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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

No definition available.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4K
-Subparagraph (c)
-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4K

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