Outstanding Exposure - Financial Guaranty Portfolio by Internal Rating (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Schedule of Insured Financial Obligations [Line Items]
Net	$ 244,013	$ 233,258
% of total net par outstanding	100.00%	100.00%
AAA
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,608	$ 3,584
% of total net par outstanding	1.50%	1.50%
AA
Schedule of Insured Financial Obligations [Line Items]
Net	$ 25,486	$ 24,383
% of total net par outstanding	10.50%	10.50%
A
Schedule of Insured Financial Obligations [Line Items]
Net	$ 113,569	$ 107,493
% of total net par outstanding	46.50%	46.10%
BBB
Schedule of Insured Financial Obligations [Line Items]
Net	$ 95,716	$ 91,906
% of total net par outstanding	39.20%	39.40%
BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 5,634	$ 5,892
% of total net par outstanding	2.30%	2.50%
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 233,981	$ 224,099
Public finance | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 186,323	$ 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	$ 47,658	$ 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	$ 2,038	$ 1,967
% of total net par outstanding	4.30%	4.40%
Public finance | AA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 17,452	$ 16,241
% of total net par outstanding	9.40%	9.10%
Public finance | AA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,442	$ 3,497
% of total net par outstanding	7.20%	7.90%
Public finance | A | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 100,267	$ 96,807
% of total net par outstanding	53.80%	53.90%
Public finance | A | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 11,005	$ 9,271
% of total net par outstanding	23.10%	20.90%
Public finance | BBB | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 64,852	$ 62,570
% of total net par outstanding	34.80%	34.80%
Public finance | BBB | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 30,147	$ 28,747
% of total net par outstanding	63.20%	64.60%
Public finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 4,566	$ 4,777
Public finance | BIG | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 3,540	$ 3,796
% of total net par outstanding	1.90%	2.10%
Public finance | BIG | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 1,026	$ 981
% of total net par outstanding	2.20%	2.20%
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 10,032	$ 9,159
Structured finance | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 8,827	$ 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	$ 1,205	$ 931
% of total net par outstanding	100.00%	100.00%
Structured finance | AAA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 884	$ 926
% of total net par outstanding	10.00%	11.20%
Structured finance | AAA | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 474	$ 469
% of total net par outstanding	39.30%	50.40%
Structured finance | AA | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 4,580	$ 4,633
% of total net par outstanding	51.90%	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	$ 1,684	$ 1,075
% of total net par outstanding	19.10%	13.10%
Structured finance | A | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 613	$ 340
% of total net par outstanding	50.90%	36.50%
Structured finance | BBB | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 611	$ 479
% of total net par outstanding	6.90%	5.80%
Structured finance | BBB | Non-U.S. public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 106	$ 110
% of total net par outstanding	8.80%	11.80%
Structured finance | BIG
Schedule of Insured Financial Obligations [Line Items]
Net	$ 1,068	$ 1,115
Structured finance | BIG | United States
Schedule of Insured Financial Obligations [Line Items]
Net	$ 1,068	$ 1,115
% of total net par outstanding	12.10%	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%