Outstanding Exposure - Additional Information (Details) $ in Millions			9 Months Ended
	Jul. 10, 2024	Jun. 26, 2023 USD ($)	Sep. 30, 2024 USD ($) Category	Dec. 31, 2023 USD ($)
Schedule of Insured Financial Obligations [Line Items]
Number of surveillance categories | Category			3
Loss Mitigation Securities			$ 1,200	$ 1,200
Net par outstanding			258,196	249,153
Fixed-maturity securities, trading			163	318
Puerto Rico Electric Power Authority | Guarantee Obligations
Schedule of Insured Financial Obligations [Line Items]
Damages sought, estimate		$ 2,400
Damages sought		$ 8,500
Stay implemented	60 days
Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			851	1,105
Puerto Rico | Puerto Rico Defaulted Exposures Subject to a Plan Support Agreement | Puerto Rico Electric Power Authority
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			531	624
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			228	372
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | PRHTA
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			228	372
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			247,920	239,296
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			10,276	9,857
Aircraft residual value insurance (RVI)
Schedule of Insured Financial Obligations [Line Items]
Residual value insurance policies exposure downgraded			308	355
Net Exposure			176	200
Commitment to Provide Guarantees | Public finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties			1,600
Potential future commitment				353
Commitment to Provide Guarantees | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties			$ 2,200
Potential future commitment				50
BIG
Schedule of Insured Financial Obligations [Line Items]
Maximum period of liquidity claims (in years)			1 year
Net par outstanding			$ 10,650	5,437
BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			9,739	4,402
BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding			911	1,035
BIG | Aircraft residual value insurance (RVI)
Schedule of Insured Financial Obligations [Line Items]
Residual value insurance policies exposure downgraded			144	144
Net Exposure			$ 84	$ 84
Minimum
Schedule of Insured Financial Obligations [Line Items]
Probability of paying more claims than being reimbursed (as a percent)			50.00%