Outstanding Exposure - Puerto Rico Net Par Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2023	Aug. 31, 2023	Dec. 31, 2022
Schedule of Insured Financial Obligations [Line Items]
Net	$ 241,833	$ 108	$ 233,258
Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net	1,105		1,361
Puerto Rico | Other Puerto Rico Exposure
Schedule of Insured Financial Obligations [Line Items]
Net	109		132
Puerto Rico | Other Puerto Rico Exposure | MFA
Schedule of Insured Financial Obligations [Line Items]
Net	108		131
Puerto Rico | Other Puerto Rico Exposure | PRASA and U of PR
Schedule of Insured Financial Obligations [Line Items]
Net	1		1
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	624		720
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement
Schedule of Insured Financial Obligations [Line Items]
Net	372		509
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | Puerto Rico Transportation Authority
Schedule of Insured Financial Obligations [Line Items]
Net	244		298
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | Puerto Rico Highways Authority
Schedule of Insured Financial Obligations [Line Items]
Net	128		182
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | Commonwealth of Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net	0		25
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | PBA
Schedule of Insured Financial Obligations [Line Items]
Net	$ 0		$ 4