Outstanding Exposure - Puerto Rico Net Par Outstanding (Details) - USD ($) $ in Millions	Jan. 31, 2024	Dec. 31, 2023	Aug. 31, 2023	Dec. 31, 2022
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		$ 249,153	$ 108	$ 233,258
Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		1,105		1,361
Puerto Rico | Puerto Rico Defaulted Exposures Subject to a Plan Support Agreement
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		624		720
Puerto Rico | Puerto Rico Defaulted Exposures Subject to a Plan Support Agreement | PREPA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		624		720
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		372		509
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | Subsequent Event
Schedule of Insured Financial Obligations [Line Items]
Principal amount, paid down	$ 144
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | PRHTA (Transportation revenue)
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		244		298
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | PRHTA (Highway revenue)
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		128		182
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | Commonwealth of Puerto Rico - GO
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		0		25
Puerto Rico | Puerto Rico Resolved Exposures Subject to a Plan Support Agreement | PBA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		0		4
Puerto Rico | Other Puerto Rico Exposures
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		109		132
Puerto Rico | Other Puerto Rico Exposures | MFA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		108		131
Puerto Rico | Other Puerto Rico Exposures | PRAASA and U of PR
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding		$ 1		$ 1