Outstanding Exposure - Debt Service Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 366,788	$ 366,692
Net Debt Service Outstanding	366,373	366,233
Public finance
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	356,459	356,078
Net Debt Service Outstanding	356,075	355,649
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	10,329	10,614
Net Debt Service Outstanding	$ 10,298	$ 10,584