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Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions | Sep. 30, 2023 | Aug. 31, 2023 | Dec. 31, 2022
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Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 241,833 | $ 108 | $ 233,258
% of total net par outstanding | 100.00% |  | 100.00%
AAA |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 3,533 |  | $ 3,584
% of total net par outstanding | 1.50% |  | 1.50%
AA |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 24,849 |  | $ 24,383
% of total net par outstanding | 10.30% |  | 10.50%
A |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 114,288 |  | $ 107,493
% of total net par outstanding | 47.20% |  | 46.10%
BBB |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 93,989 |  | $ 91,906
% of total net par outstanding | 38.90% |  | 39.40%
BIG |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 5,174 |  | $ 5,892
% of total net par outstanding | 2.10% |  | 2.50%
Public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 231,721 |  | $ 224,099
Public finance | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 185,973 |  | $ 179,636
% of total net par outstanding | 100.00% |  | 100.00%
Public finance | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 45,748 |  | $ 44,463
% of total net par outstanding | 100.00% |  | 100.00%
Public finance | AAA | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 212 |  | $ 222
% of total net par outstanding | 0.10% |  | 0.10%
Public finance | AAA | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 2,004 |  | $ 1,967
% of total net par outstanding | 4.40% |  | 4.40%
Public finance | AA | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 16,994 |  | $ 16,241
% of total net par outstanding | 9.10% |  | 9.10%
Public finance | AA | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 3,298 |  | $ 3,497
% of total net par outstanding | 7.20% |  | 7.90%
Public finance | A | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 101,243 |  | $ 96,807
% of total net par outstanding | 54.50% |  | 53.90%
Public finance | A | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 10,545 |  | $ 9,271
% of total net par outstanding | 23.10% |  | 20.90%
Public finance | BBB | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 64,220 |  | $ 62,570
% of total net par outstanding | 34.50% |  | 34.80%
Public finance | BBB | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 29,083 |  | $ 28,747
% of total net par outstanding | 63.50% |  | 64.60%
Public finance | BIG |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 4,122 |  | $ 4,777
Public finance | BIG | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 3,304 |  | $ 3,796
% of total net par outstanding | 1.80% |  | 2.10%
Public finance | BIG | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 818 |  | $ 981
% of total net par outstanding | 1.80% |  | 2.20%
Structured finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 10,112 |  | $ 9,159
Structured finance | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 8,975 |  | $ 8,228
% of total net par outstanding | 100.00% |  | 100.00%
Structured finance | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 1,137 |  | $ 931
% of total net par outstanding | 100.00% |  | 100.00%
Structured finance | AAA | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 860 |  | $ 926
% of total net par outstanding | 9.60% |  | 11.20%
Structured finance | AAA | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 457 |  | $ 469
% of total net par outstanding | 40.20% |  | 50.40%
Structured finance | AA | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 4,545 |  | $ 4,633
% of total net par outstanding | 50.70% |  | 56.30%
Structured finance | AA | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 12 |  | $ 12
% of total net par outstanding | 1.00% |  | 1.30%
Structured finance | A | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 1,932 |  | $ 1,075
% of total net par outstanding | 21.50% |  | 13.10%
Structured finance | A | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 568 |  | $ 340
% of total net par outstanding | 50.00% |  | 36.50%
Structured finance | BBB | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 586 |  | $ 479
% of total net par outstanding | 6.50% |  | 5.80%
Structured finance | BBB | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 100 |  | $ 110
% of total net par outstanding | 8.80% |  | 11.80%
Structured finance | BIG |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 1,052 |  | $ 1,115
Structured finance | BIG | United States |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 1,052 |  | $ 1,115
% of total net par outstanding | 11.70% |  | 13.60%
Structured finance | BIG | Non-U.S. public finance |  |  |
Schedule of Insured Financial Obligations [Line Items] |  |  |
Net | $ 0 |  | $ 0
% of total net par outstanding | 0.00% |  | 0.00%

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