Outstanding Exposure - BIG Net Par Outstanding (Details) $ in Millions	Mar. 31, 2023 USD ($) risk	Dec. 31, 2022 USD ($) risk
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, credit derivative	$ 3,262	$ 3,203
Net	236,383	233,258
BIG
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	5,826	5,835
Net par outstanding, credit derivative	56	57
Net	$ 5,882	$ 5,892
Number of risks, financial guaranty insurance | risk	241	247
Number of risks, credit derivative | risk	11	13
Number of risks | risk	252	260
BIG | BIG 1
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	$ 3,370	$ 3,357
Net par outstanding, credit derivative	6	6
Net	$ 3,376	$ 3,363
Number of risks, financial guaranty insurance | risk	117	122
Number of risks, credit derivative | risk	1	1
Number of risks | risk	118	123
BIG | BIG 2
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	$ 170	$ 171
Net par outstanding, credit derivative	10	10
Net	$ 180	$ 181
Number of risks, financial guaranty insurance | risk	15	14
Number of risks, credit derivative | risk	2	2
Number of risks | risk	17	16
BIG | BIG 3
Schedule of Insured Financial Obligations [Line Items]
Net par outstanding, financial guaranty insurance	$ 2,286	$ 2,307
Net par outstanding, credit derivative	40	41
Net	$ 2,326	$ 2,348
Number of risks, financial guaranty insurance | risk	109	111
Number of risks, credit derivative | risk	8	10
Number of risks | risk	117	121