Outstanding Exposure - Puerto Rico Net Par Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Schedule of Insured Financial Obligations [Line Items]
Net	$ 227,071	$ 236,392
Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net	2,071	3,572
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement
Schedule of Insured Financial Obligations [Line Items]
Net	1,218	2,643
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | Commonwealth of Puerto Rico
Schedule of Insured Financial Obligations [Line Items]
Net	25	1,097
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PBA
Schedule of Insured Financial Obligations [Line Items]
Net	4	122
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | GO/PBA PSA
Schedule of Insured Financial Obligations [Line Items]
Net	29	1,219
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PRHTA (Transportation revenue)
Schedule of Insured Financial Obligations [Line Items]
Net	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	418	457
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PRCCDA
Schedule of Insured Financial Obligations [Line Items]
Net	0	152
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | HTA/CCDA PSA
Schedule of Insured Financial Obligations [Line Items]
Net	1,189	1,408
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PRIFA
Schedule of Insured Financial Obligations [Line Items]
Net	0	16
Puerto Rico | Puerto Rico Exposures Subject to a Plan or Support Agreement | PREPA
Schedule of Insured Financial Obligations [Line Items]
Net	720	748
Puerto Rico | Other Puerto Rico Exposures
Schedule of Insured Financial Obligations [Line Items]
Net	853	929
Puerto Rico | Other Puerto Rico Exposures | MFA
Schedule of Insured Financial Obligations [Line Items]
Net	131	179
Puerto Rico | Other Puerto Rico Exposures | PRASA and U of PR
Schedule of Insured Financial Obligations [Line Items]
Net	$ 2	$ 2