Outstanding Exposure - Components of BIG Net Par Outstanding (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Schedule of Insured Financial Obligations [Line Items]
Net	$ 232,812	$ 236,392
Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	224,095	227,164
Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	6,546	6,837
Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	8,717	9,228
BIG
Schedule of Insured Financial Obligations [Line Items]
Net	5,386	7,356
BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	4,091	5,972
BIG | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	110	119
BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,295	1,384
BIG | BIG 1
Schedule of Insured Financial Obligations [Line Items]
Net	1,821	2,443
BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,776	2,321
BIG | BIG 1 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	1
BIG | BIG 1 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	45	122
BIG | BIG 2
Schedule of Insured Financial Obligations [Line Items]
Net	244	181
BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	130	116
BIG | BIG 2 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	37	41
BIG | BIG 2 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	114	65
BIG | BIG 3
Schedule of Insured Financial Obligations [Line Items]
Net	3,321	4,732
BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,185	3,535
BIG | BIG 3 | Other structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	73	77
BIG | BIG 3 | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,136	1,197
United States | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	179,648	177,219
United States | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	2,171	2,391
United States | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	7,935	8,374
United States | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	3,570	5,372
United States | BIG | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	1,185	1,265
United States | BIG | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,295	1,384
United States | BIG | BIG 1 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	1,294	1,765
United States | BIG | BIG 1 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	45	121
United States | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	130	116
United States | BIG | BIG 2 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	77	24
United States | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	2,146	3,491
United States | BIG | BIG 3 | RMBS
Schedule of Insured Financial Obligations [Line Items]
Net	1,063	1,120
Non-U.S. public finance | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	44,447	49,945
Non-U.S. public finance | Structured finance
Schedule of Insured Financial Obligations [Line Items]
Net	782	854
Non-U.S. public finance | BIG | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	521	600
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	482	556
Non-U.S. public finance | BIG | BIG 2 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	0	0
Non-U.S. public finance | BIG | BIG 3 | Public finance
Schedule of Insured Financial Obligations [Line Items]
Net	$ 39	$ 44