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Loss And Loss Adjustment Expense Reserves (Summary Of Credit Impairments Related To Derivatives) (Narrative) (Detail) (USD $) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2013 securityloan | Jun. 30, 2012 | Jun. 30, 2013 securityloan | Jun. 30, 2012
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Discount rate of credit impairments |  |  | 5.72% |
Number of structured Cmbs commutations since 2010 |  |  | 84 |
Gross exposure commuted on Cmbs insured derivatives since 2010 |  |  | $ 41,600,000,000 |
Loan balance greater than with debt service coverage ratio | 75,000,000 |  | 75,000,000 |
Debt service coverage ratio |  |  | 1.0 |
Proprietary performance data on CRE loans, amount from 1992 to 2011 | 80,000 |  | 80,000 |
Number of representative cohorts in commercial real estate proprietary model based on debt service coverage ratio ("DSCR") and property type. |  |  | 168 |
Policyholder (Benefits) And Claims Incurred Net | 188,000,000 | 62,000,000 | (6,000,000) | 159,000,000
Additional estimated credit impairment on Cmbs derivatives |  |  | 399,000,000 |
Aggregate ITD credit impairment on Cmbs derivatives since 2010 |  |  | 4,000,000,000 |
Cmbs severities exceeded complete loss in certain instances |  |  | 100.00% |
Commercial Real Estate Collateralized Debt Obligations [Member] |  |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Policyholder (Benefits) And Claims Incurred Net |  |  | $ (38,000,000) |
Minimum [Member] |  |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Percentage of loss on liquidation |  |  | 1.00% |
Maximum [Member] |  |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Percentage of loss on liquidation |  |  | 2.00% |

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- Definition This element represents number of representative cohortsi in commercial real estate proprietary model based on debt service coverage ratio and property type + References No definition available. + Details
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- Definition Provision for benefits, claims and claims settlement expenses incurred during the period net of the effects of contracts assumed and ceded. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.5) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 5 -Article 7 + Details
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