Outstanding Exposure - Additional Information (Details) $ in Millions		9 Months Ended
	Jun. 26, 2023 USD ($)	Sep. 30, 2023 USD ($) Category	Aug. 31, 2023 USD ($)	Jun. 23, 2023 USD ($)	Dec. 31, 2022 USD ($)
Schedule of Insured Financial Obligations [Line Items]
Number of surveillance categories | Category		3
Loss Mitigation Securities		$ 1,200			$ 1,300
Net par outstanding		241,833	$ 108		233,258
Guarantor, maximum exposure		1,600
Puerto Rico Electric Power Authority
Schedule of Insured Financial Obligations [Line Items]
Plaintiff debt capacity				$ 2,500
Plaintiff debt capacity allocated to settling creditors				1,400
Plaintiff debt capacity allocated to bondholders and general unsecured creditors				$ 1,100
Claim received as restructuring bonds, percent				12.50%
Puerto Rico Electric Power Authority | Guarantee Obligations
Schedule of Insured Financial Obligations [Line Items]
Damages sought, estimate	$ 2,400
Calculated collection period	100 years
Calculated discount rate	7.00%
Calculated discounted cash flows	$ 3,000
Additional calculated riscount rate	20.00%
Damages sought	$ 8,500
Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1,105			1,361
Puerto Rico | Other Public Corporations
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		109
Puerto Rico | PRHTA
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		372
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		231,721			224,099
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		10,112			9,159
Aircraft residual value insurance (RVI)
Schedule of Insured Financial Obligations [Line Items]
Residual value insurance policies exposure downgraded		355			355
Net Exposure		200			200
Commitment to Provide Guarantees | Public finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties		1,500
Commitment to Provide Guarantees | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties		$ 1,300
BIG
Schedule of Insured Financial Obligations [Line Items]
Maximum period of liquidity claims (in years)		1 year
Net par outstanding		$ 5,174			5,892
BIG | Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1,100			1,400
BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		4,122			4,777
BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1,052			1,115
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%