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Financial Guarantees in Force - Summary of International Finance Guaranteed Portfolio (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | $ 62,716,000 | $ 79,346,000
International Finance [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 16,812,000 | 17,333,000
International Finance [Member] | United Kingdom [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 13,554,000 | 12,798,000
International Finance [Member] | Australia [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 608,000 | 1,393,000
International Finance [Member] | Italy [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 877,000 | 898,000
International Finance [Member] | Austria [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 770,000 | 696,000
International Finance [Member] | FRANCE |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 329,000 | 286,000
International Finance [Member] | Internationally Diversified [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | 368,000 | 648,000
International Finance [Member] | Other International [Member] |  |
Guarantor Obligations [Line Items] |  |
Net Par Amount Outstanding | $ 306,000 | $ 614,000

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- Definition The amount as of the balance sheet date of the participating business in force. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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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