Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Dec. 31, 2023	Aug. 31, 2023	Dec. 31, 2022
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 249,153	$ 108	$ 233,258
% of total net par outstanding	100.00%		100.00%
AAA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 3,504		$ 3,584
% of total net par outstanding	1.40%		1.50%
AA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 25,868		$ 24,383
% of total net par outstanding	10.40%		10.50%
A
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 118,123		$ 107,493
% of total net par outstanding	47.40%		46.10%
BBB
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 96,221		$ 91,906
% of total net par outstanding	38.60%		39.40%
BIG
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 5,437		$ 5,892
% of total net par outstanding	2.20%		2.50%
U.S.
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 198,921
Non U.S.
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	50,232
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	239,296		$ 224,099
Public finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	4,402		4,777
Public finance | U.S.
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 190,289		$ 179,636
% of total net par outstanding	100.00%		100.00%
Public finance | U.S. | AAA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 110		$ 222
% of total net par outstanding	0.10%		0.10%
Public finance | U.S. | AA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 17,883		$ 16,241
% of total net par outstanding	9.40%		9.10%
Public finance | U.S. | A
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 102,945		$ 96,807
% of total net par outstanding	54.10%		53.90%
Public finance | U.S. | BBB
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 66,080		$ 62,570
% of total net par outstanding	34.70%		34.80%
Public finance | U.S. | BIG
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 3,271		$ 3,796
% of total net par outstanding	1.70%		2.10%
Public finance | Non U.S.
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 49,007		$ 44,463
% of total net par outstanding	100.00%		100.00%
Public finance | Non U.S. | AAA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 2,062		$ 1,967
% of total net par outstanding	4.20%		4.40%
Public finance | Non U.S. | AA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 3,379		$ 3,497
% of total net par outstanding	6.90%		7.90%
Public finance | Non U.S. | A
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 12,968		$ 9,271
% of total net par outstanding	26.50%		20.90%
Public finance | Non U.S. | BBB
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 29,467		$ 28,747
% of total net par outstanding	60.10%		64.60%
Public finance | Non U.S. | BIG
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 1,131		$ 981
% of total net par outstanding	2.30%		2.20%
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 9,857		$ 9,159
Structured finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	1,035		1,115
Structured finance | U.S.
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 8,632		$ 8,228
% of total net par outstanding	100.00%		100.00%
Structured finance | U.S. | AAA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 867		$ 926
% of total net par outstanding	10.00%		11.20%
Structured finance | U.S. | AA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 4,517		$ 4,633
% of total net par outstanding	52.30%		56.30%
Structured finance | U.S. | A
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 1,639		$ 1,075
% of total net par outstanding	19.00%		13.10%
Structured finance | U.S. | BBB
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 574		$ 479
% of total net par outstanding	6.70%		5.80%
Structured finance | U.S. | BIG
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 1,035		$ 1,115
% of total net par outstanding	12.00%		13.60%
Structured finance | Non U.S.
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 1,225		$ 931
% of total net par outstanding	100.00%		100.00%
Structured finance | Non U.S. | AAA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 465		$ 469
% of total net par outstanding	38.00%		50.40%
Structured finance | Non U.S. | AA
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 89		$ 12
% of total net par outstanding	7.30%		1.30%
Structured finance | Non U.S. | A
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 571		$ 340
% of total net par outstanding	46.60%		36.50%
Structured finance | Non U.S. | BBB
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 100		$ 110
% of total net par outstanding	8.10%		11.80%
Structured finance | Non U.S. | BIG
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding	$ 0		$ 0
% of total net par outstanding	0.00%		0.00%