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Loss And Loss Adjustment Expense Reserves (Summary Of Credit Impairments Related To Derivatives) (Narrative) (Details) (USD $) | 6 Months Ended
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Jun. 30, 2011
Discount rate of credit impairments | 5.93%
Additional estimated credit impairment on derivatives | $ 363,000,000
Aggregate credit impairment on derivatives | 1,500,000,000
Number of structured derivatives | 22
Exposed gross insured derivatives | 10,300,000,000
Life of loans, minimum | 6Y
Life of loans, maximum | 7Y
Maximum loans with debt service coverage ratio | 75,000,000
Debt service coverage ratio | 1.0
Percentage of loans greater than ninety days | 75.00%
Percentage of loans liquidated | 65.00%
Percentage of loans modified | 35.00%
Weighted loss estimate | $ 1,500,000,000
Percentage of properties held in pools | 68.00%
Maximum Range [Member] |
Percentage of loss on liquidation | 2.00%
Minimum Range [Member] |
Percentage of loss on liquidation | 1.00%

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