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Financial Guarantees in Force - Summary of International Finance Guaranteed Portfolio (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | $ 33,888 | $ 38,018
International Finance [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 12,054 | 12,857
International Finance [Member] | United Kingdom [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 9,711 | 10,593
International Finance [Member] | Australia [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 420 | 382
International Finance [Member] | Italy [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 803 | 767
International Finance [Member] | Austria [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 707 | 674
International Finance [Member] | FRANCE |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 277 | 303
International Finance [Member] | Other International [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | $ 136 | $ 138

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- Definition Amount of participating insurance in force. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 50 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6483535&loc=d3e16392-158451 + Details
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