Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts Earned Premiums by Geographic Location (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums Earned, Net, Financial Guarantee Insurance Contracts	$ 56	$ 47	$ 54
Premiums Receivable, Gross	259	329
Liability for Claims and Claims Adjustment Expense	805	1,570
Subrogation recoverable	271	2,092
Property and Casualty, Commercial Insurance
Liability for Claims and Claims Adjustment Expense	90	32
Public Finance [Member]
Premiums Receivable, Gross	150	159
Structured Finance [Member]
Premiums Receivable, Gross	24	45
International Finance [Member]
Premiums Receivable, Gross	85	125
Housing Revenue [Member] \| Public Finance [Member]
Premiums Receivable, Gross	148	157
Other Public Finance Sectors [Member] \| Public Finance [Member]
Premiums Receivable, Gross	2	2
Mortgage-backed and Home Equity [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	11	16
Student Loan [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	8	12
Structured Insurance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	10
Other Structured Finance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	4	7
Sovereign/Sub-sovereign [Member] \| International Finance [Member]
Premiums Receivable, Gross	64	93
Investor-owned and Public Utilities [Member] \| International Finance [Member]
Premiums Receivable, Gross	18	28
Other International [Member] \| International Finance [Member]
Premiums Receivable, Gross	2	5
Surveillance Category One [Member]
Premiums Receivable, Gross	217	277
Surveillance Category One [Member] \| Public Finance [Member]
Premiums Receivable, Gross	142	151
Surveillance Category One [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	5	19
Surveillance Category One [Member] \| International Finance [Member]
Premiums Receivable, Gross	70	107
Surveillance Category One [Member] \| Housing Revenue [Member] \| Public Finance [Member]
Premiums Receivable, Gross	140	149
Surveillance Category One [Member] \| Other Public Finance Sectors [Member] \| Public Finance [Member]
Premiums Receivable, Gross	2	2
Surveillance Category One [Member] \| Mortgage-backed and Home Equity [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	1
Surveillance Category One [Member] \| Student Loan [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	1	1
Surveillance Category One [Member] \| Structured Insurance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	10
Surveillance Category One [Member] \| Other Structured Finance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	4	7
Surveillance Category One [Member] \| Sovereign/Sub-sovereign [Member] \| International Finance [Member]
Premiums Receivable, Gross	49	74
Surveillance Category One [Member] \| Investor-owned and Public Utilities [Member] \| International Finance [Member]
Premiums Receivable, Gross	18	28
Surveillance Category One [Member] \| Other International [Member] \| International Finance [Member]
Premiums Receivable, Gross	2	5
IA [Member]
Premiums Receivable, Gross	10	12
IA [Member] \| Public Finance [Member]
Premiums Receivable, Gross	3	3
IA [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	1	1
IA [Member] \| International Finance [Member]
Premiums Receivable, Gross	7	8
IA [Member] \| Housing Revenue [Member] \| Public Finance [Member]
Premiums Receivable, Gross	3	3
IA [Member] \| Other Public Finance Sectors [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
IA [Member] \| Mortgage-backed and Home Equity [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
IA [Member] \| Student Loan [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	1	1
IA [Member] \| Structured Insurance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
IA [Member] \| Other Structured Finance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
IA [Member] \| Sovereign/Sub-sovereign [Member] \| International Finance [Member]
Premiums Receivable, Gross	7	8
IA [Member] \| Investor-owned and Public Utilities [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
IA [Member] \| Other International [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
II [Member]
Premiums Receivable, Gross	5	6
II [Member] \| Public Finance [Member]
Premiums Receivable, Gross	5	5
II [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	1
II [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
II [Member] \| Housing Revenue [Member] \| Public Finance [Member]
Premiums Receivable, Gross	5	5
II [Member] \| Other Public Finance Sectors [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
II [Member] \| Mortgage-backed and Home Equity [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	1
II [Member] \| Student Loan [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
II [Member] \| Structured Insurance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
II [Member] \| Other Structured Finance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
II [Member] \| Sovereign/Sub-sovereign [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
II [Member] \| Investor-owned and Public Utilities [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
II [Member] \| Other International [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
III [Member]
Premiums Receivable, Gross	16	22
III [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
III [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	7	12
III [Member] \| International Finance [Member]
Premiums Receivable, Gross	9	11
III [Member] \| Housing Revenue [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
III [Member] \| Other Public Finance Sectors [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
III [Member] \| Mortgage-backed and Home Equity [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	2
III [Member] \| Student Loan [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	7	9
III [Member] \| Structured Insurance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
III [Member] \| Other Structured Finance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
III [Member] \| Sovereign/Sub-sovereign [Member] \| International Finance [Member]
Premiums Receivable, Gross	9	11
III [Member] \| Investor-owned and Public Utilities [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
III [Member] \| Other International [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member]
Premiums Receivable, Gross	11	12
IV [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	11	12
IV [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Housing Revenue [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Other Public Finance Sectors [Member] \| Public Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Mortgage-backed and Home Equity [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	11	12
IV [Member] \| Student Loan [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Structured Insurance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Other Structured Finance [Member] \| Structured Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Sovereign/Sub-sovereign [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Investor-owned and Public Utilities [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
IV [Member] \| Other International [Member] \| International Finance [Member]
Premiums Receivable, Gross	0	0
Reportable Geographical Components [Member] \| UNITED STATES
Premiums Earned, Net, Financial Guarantee Insurance Contracts	41	27	32
Reportable Geographical Components [Member] \| UNITED KINGDOM
Premiums Earned, Net, Financial Guarantee Insurance Contracts	13	14	24
Reportable Geographical Components [Member] \| Other International [Member]
Premiums Earned, Net, Financial Guarantee Insurance Contracts	$ 3	$ 6	$ (2)

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (cc)
-URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

+ Details

Name:	us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after premiums ceded to other entities and premiums assumed by the entity, of financial guarantee premiums earned.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=84167274&loc=d3e27175-158546

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 7
-URI https://asc.fasb.org/extlink&oid=6933001&loc=SL5747862-161289

Reference 3: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=99397103&loc=d3e6816-158387

Reference 4: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI https://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 5: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 6: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI https://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 7: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(1))
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 8: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=99397103&loc=d3e6811-158387

+ Details

Name:	us-gaap_PremiumsEarnedNetFinancialGuaranteeInsuranceContracts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Gross amount, as of the balance sheet date, due the entity from (a) agents and insureds, (b) uncollected premiums and (c) others, before deducting the allowance for doubtful accounts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.5)
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

+ Details

Name:	us-gaap_PremiumsReceivableGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The estimated amount as of the balance sheet date to be received by an insurer from the sale of property (usually damaged) on which the insurer has paid a total claim to the insured and has obtained title to the property and the right of an insurer to pursue any course of recovery of damages, in its name or in the name of the policyholder, against a third party who is liable for costs relating to an insured event that have been paid by the insurer. Estimated salvage and subrogation is generally deducted from the liability for unpaid claims.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 30
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=6482241&loc=d3e13783-158432

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 30
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=6482241&loc=d3e13779-158432

+ Details

Name:	us-gaap_SalvageAndSubrogationRecoveriesValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant