Outstanding Exposure - Components of BIG Net Par Outstanding (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Schedule of Insured Financial Obligations [Line Items]
Net	$ 254,396	$ 249,153
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	244,176	239,296
Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	8,635	8,083
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	10,220	9,857
BIG
Schedule of Insured Financial Obligations [Line Items]
Net	5,502	5,437
BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	4,575	4,402
BIG | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	82	94
BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	927	1,035
BIG | BIG 1
Schedule of Insured Financial Obligations [Line Items]
Net	2,170	2,410
BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,154	2,388
BIG | BIG 1 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
BIG | BIG 1 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	16	22
BIG | BIG 2
Schedule of Insured Financial Obligations [Line Items]
Net	1,529	989
BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,477	926
BIG | BIG 2 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	23	27
BIG | BIG 2 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	52	63
BIG | BIG 3
Schedule of Insured Financial Obligations [Line Items]
Net	1,803	2,038
BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	944	1,088
BIG | BIG 3 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	59	67
BIG | BIG 3 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	859	950
United States | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	194,593	190,289
United States | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	1,585	1,774
United States | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	8,759	8,632
United States | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	3,490	3,271
United States | BIG | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	845	941
United States | BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	927	1,035
United States | BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,594	1,257
United States | BIG | BIG 1 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	16	22
United States | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	952	926
United States | BIG | BIG 2 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	29	36
United States | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	944	1,088
United States | BIG | BIG 3 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	800	883
Non-U.S. public finance | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	49,583	49,007
Non-U.S. public finance | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,461	1,225
Non-U.S. public finance | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,085	1,131
Non-U.S. public finance | BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
Non-U.S. public finance | BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	560	1,131
Non-U.S. public finance | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	525	0
Non-U.S. public finance | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 0	$ 0