Outstanding Exposure - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Aug. 31, 2021	Sep. 30, 2022	Oct. 12, 2022	Mar. 15, 2022	Jan. 18, 2022	Dec. 31, 2021
Schedule of Insured Financial Obligations [Line Items]
Loss mitigation securities and other		$ 1,300				$ 1,300
Net par outstanding		227,071				236,392
Residual value insurance policies exposure downgraded		1,656				1,605
Net Exposure		1,169				1,071
Guarantor, maximum exposure		232
Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		2,071				3,572
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1,218				2,643
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | GO/PBA PSA
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		29				1,219
Net par outstanding, portion of noncallable insured bonds						102
Cash received net of outbound reinsurance				$ 530
Recovery bonds received, net				605
Contingent value instruments received, net				258
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | Commonwealth of Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		25				1,097
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | Puerto Rico Public Buildings Authority
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		4				122
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | HTA/CCDA PSA
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1,189				1,408
Net par outstanding, portion of noncallable insured bonds		788
Outstanding principal amount of amended plan election, net		451
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PRHTA (Transportation revenue)
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		771				799
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PRHTA (Highway revenue)
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		418				457
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | Puerto Rico Convention Center District Authority
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		0				152
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PREPA
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		720				748
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PRIFA
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		0				16
Puerto Rico | Constitutionally Guaranteed | Commonwealth of Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Litigation amount					$ 35,000
Puerto Rico | Constitutionally Guaranteed | Commonwealth of Puerto Rico | Subsequent Event
Schedule of Insured Financial Obligations [Line Items]
Litigation amount			$ 6,400
Puerto Rico | Constitutionally Guaranteed | GO and PBA POA
Schedule of Insured Financial Obligations [Line Items]
Amount of outstanding principal to be paid, in percent	100.00%
Puerto Rico | Constitutionally Guaranteed | PRCCDA and PRIFA
Schedule of Insured Financial Obligations [Line Items]
Cash received for bonds				47
Notional amount of contingent value instrument received for bonds				$ 98
Puerto Rico | Pension Obligations | Commonwealth of Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Litigation amount					$ 50,000
Puerto Rico | Other Public Corporations | University of Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1
Puerto Rico | Other Public Corporations | PRASA (Puerto Rico Aqueduct and Sewer Authority)
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1
Puerto Rico | PRHTA
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		1,200
Cash received		147
Notional amount of contingent value instrument received		672
U.S. Virgin Islands
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		183
Principal amount defeased		256
Principal amount upgraded (downgraded)		134
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		218,905				227,164
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		8,166				9,228
Commitment to Provide Guarantees | Public finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties		893
Commitment to Provide Guarantees | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Outstanding commitments to provide guaranties		$ 741
BIG
Schedule of Insured Financial Obligations [Line Items]
Maximum period of liquidity claims (in years)		1 year
Net par outstanding		$ 5,785				7,356
Residual value insurance policies exposure downgraded		144				144
Net Exposure		84				84
BIG | Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		2,100				3,600
Decrease in net par outstanding		1,500
BIG | U.S. Virgin Islands
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		47				469
BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		4,649				5,972
BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding		$ 1,136				$ 1,384
Minimum
Schedule of Insured Financial Obligations [Line Items]
Probability of paying more claims than being reimbursed (as a percent)		50.00%