Outstanding Exposure - BIG Net Par Outstanding (Details) $ in Millions	Dec. 31, 2021 USD ($) risk	Dec. 31, 2020 USD ($) risk
Schedule of Insured Financial Obligations [Line Items]
Credit derivative, net par outstanding	$ 4,040	$ 5,371
Total net par outstanding	$ 236,392	234,153
Number of Risks | risk	7,848
BIG
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	$ 7,293	7,855
Credit derivative, net par outstanding	63	120
Total net par outstanding	$ 7,356	$ 7,975
Number of risks, financial guaranty insurance | risk	262	270
Number of risks, credit derivative | risk	11	14
Number of Risks | risk	273	284
BIG | BIG 1
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	$ 2,429	$ 2,781
Credit derivative, net par outstanding	14	70
Total net par outstanding	$ 2,443	$ 2,851
Number of risks, financial guaranty insurance | risk	117	125
Number of risks, credit derivative | risk	2	6
Number of Risks | risk	119	131
BIG | BIG 2
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	$ 177	$ 130
Credit derivative, net par outstanding	4	4
Total net par outstanding	$ 181	$ 134
Number of risks, financial guaranty insurance | risk	16	19
Number of risks, credit derivative | risk	1	1
Number of Risks | risk	17	20
BIG | BIG 3
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	$ 4,687	$ 4,944
Credit derivative, net par outstanding	45	46
Total net par outstanding	$ 4,732	$ 4,990
Number of risks, financial guaranty insurance | risk	129	126
Number of risks, credit derivative | risk	8	7
Number of Risks | risk	137	133