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Financial Guarantees in Force - Summary of Financial Guarantee Portfolio Diversification by Type of Guaranteed Bond (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 19,541	$ 22,613
Total Net Par Outstanding Does Not Exceed This Percentage in Any of the States in the US	6.00%
Highest single insured risk of aggregate net par amount guaranteed	4.60%
Public Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 7,562	10,547
Public Finance [Member] | Lease and Tax-backed Revenue [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,542	1,979
Public Finance [Member] | General Obligation [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,051	1,301
Public Finance [Member] | Housing Revenue [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	3,443	5,491
Public Finance [Member] | Housing Revenue [Member] | Military Housing [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	3,371	5,400
Public Finance [Member] | Other [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,526	1,776
Structured Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	3,315	3,612
Structured Finance [Member] | Mortgage-backed and Home Equity [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,712	1,930
Structured Finance [Member] | Investor-owned Utilities [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	1,077	1,103
Structured Finance [Member] | Other Structured Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	526	579
International Finance [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	8,664	8,454
International Finance [Member] | Asset Backed and Other [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	862	1,083
International Finance [Member] | Investor-owned and Public Utilities [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	2,855	2,583
International Finance [Member] | Sovereign/Sub-sovereign [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	4,221	4,077
International Finance [Member] | Transportation [Member]
Guarantor Obligations [Line Items]
Net Par Amount Outstanding	$ 726	$ 711

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Percentage of highest single insured risk of aggregate net par amount guaranteed

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
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-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
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-Section 50
-Paragraph 4
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
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