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Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) (USD $) In Millions, unless otherwise specified | 6 Months Ended
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Jun. 30, 2012 | Jun. 30, 2011
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Changes in Unearned Premium Revenue | $ 311 | $ 361
Changes in LAE Reserves | (2) | (265)
Loss And LAE Reserves [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Gross Loss and LAE Reserve as of December 31, 2011 | 836 |
Loss Payments for Cases with Reserves | (222) |
Accretion of Claim Liability Discount | 6 |
Changes in Discount Rates | 23 |
Changes in Timing of Payments | 55 |
Changes in Amount of Net Payments | (1) |
Changes in Assumptions | 112 |
Changes in Unearned Premium Revenue | 1 |
Changes in LAE Reserves | 25 |
Gross Loss and LAE Reserve as of June 30, 2012 | $ 835 |

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- Definition This element represents the amount of the change in the claim liability related to financial guarantee insurance contracts arising from a change in the amount of net payments of claim liability. + References No definition available. + Details
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Period Type: | duration

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- Definition Financial Guarantee Insurance Contracts Claim Liability Significant Components Of Change In Assumptions + References No definition available. + Details
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- Details
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- Definition Loss payments for cases with reserves + References No definition available. + Details
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- Definition This element represents the amount of the change in the claim liability related to financial guarantee insurance contracts arising from the accretion of the discount of the claim liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 163 -Paragraph 30 -Subparagraph f(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 9 -Subparagraph (a)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292 + Details
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- Definition This element represents the amount of change in the claim liability related to financial guarantee insurance contracts arising from a change in the rate used to discount the claim liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 9 -Subparagraph (a)(2)(i) -URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 163 -Paragraph 30 -Subparagraph f(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition This element represents the amount of the change in the claim liability related to financial guarantee insurance contracts arising from a change in the timing of the claim liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 163 -Paragraph 30 -Subparagraph f(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 9 -Subparagraph (a)(2)(iii) -URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292 + Details
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- Definition The increase (decrease) during the reporting period in the reserve account established to account for expected but unspecified losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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- Definition Change during the period in the unearned portion of premiums written, excluding the portion amortized into income. Premiums written are initially booked as unearned premiums and are recognized as revenue over the known or estimated life of the policy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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- Definition Alternate concept name for the aggregate amount of policy reserves (provided for future obligations including unpaid claims and claims adjustment expenses) and policy benefits (liability for future policy benefits) as of the balance sheet date; grouped amount of all the liabilities associated with the company's insurance policies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 94-5 -Paragraph 11 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13(a)(1)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 5 -Paragraph 9 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph a -Article 7 + Details
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