Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Schedule of Insured Financial Obligations [Line Items]
Net	$ 254,396	$ 249,153
% of total net par outstanding	100.00%	100.00%
AAA
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,220	$ 3,504
% of total net par outstanding	1.20%	1.40%
AA
Schedule of Insured Financial Obligations [Line Items]
Net	$ 26,961	$ 25,868
% of total net par outstanding	10.60%	10.40%
A
Schedule of Insured Financial Obligations [Line Items]
Net	$ 121,607	$ 118,123
% of total net par outstanding	47.80%	47.40%
BBB
Schedule of Insured Financial Obligations [Line Items]
Net	$ 97,106	$ 96,221
% of total net par outstanding	38.20%	38.60%
BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 5,502	$ 5,437
% of total net par outstanding	2.20%	2.20%
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 244,176	$ 239,296
Public finance | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 194,593	$ 190,289
% of total net par outstanding	100.00%	100.00%
Public finance | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 49,583	$ 49,007
% of total net par outstanding	100.00%	100.00%
Public finance | AAA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 27	$ 110
% of total net par outstanding	0.00%	0.10%
Public finance | AAA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 2,066	$ 2,062
% of total net par outstanding	4.20%	4.20%
Public finance | AA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 18,100	$ 17,883
% of total net par outstanding	9.30%	9.40%
Public finance | AA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,164	$ 3,379
% of total net par outstanding	6.30%	6.90%
Public finance | A | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 106,415	$ 102,945
% of total net par outstanding	54.70%	54.10%
Public finance | A | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 13,437	$ 12,968
% of total net par outstanding	27.10%	26.50%
Public finance | BBB | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 66,561	$ 66,080
% of total net par outstanding	34.20%	34.70%
Public finance | BBB | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 29,831	$ 29,467
% of total net par outstanding	60.20%	60.10%
Public finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 4,575	$ 4,402
Public finance | BIG | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,490	$ 3,271
% of total net par outstanding	1.80%	1.70%
Public finance | BIG | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 1,085	$ 1,131
% of total net par outstanding	2.20%	2.30%
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 10,220	$ 9,857
Structured finance | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 8,759	$ 8,632
% of total net par outstanding	100.00%	100.00%
Structured finance | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 1,461	$ 1,225
% of total net par outstanding	100.00%	100.00%
Structured finance | AAA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 682	$ 867
% of total net par outstanding	7.80%	10.00%
Structured finance | AAA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 445	$ 465
% of total net par outstanding	30.50%	38.00%
Structured finance | AA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 5,623	$ 4,517
% of total net par outstanding	64.20%	52.30%
Structured finance | AA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 74	$ 89
% of total net par outstanding	5.00%	7.30%
Structured finance | A | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 902	$ 1,639
% of total net par outstanding	10.30%	19.00%
Structured finance | A | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 853	$ 571
% of total net par outstanding	58.40%	46.60%
Structured finance | BBB | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 625	$ 574
% of total net par outstanding	7.10%	6.70%
Structured finance | BBB | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 89	$ 100
% of total net par outstanding	6.10%	8.10%
Structured finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 927	$ 1,035
Structured finance | BIG | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 927	$ 1,035
% of total net par outstanding	10.60%	12.00%
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%