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Investments (Summary Of Significant Inputs Considered In Determining The Measurement Of Credit Losses On Securities) (Detail)
 6 Months Ended
Jun. 30, 2012
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]  
Expected size of losses, Weighted average 92.10% [1],[2]
Current subordination levels, Weighted average 0.00% [2],[3]
Prepayment speed (annual constant prepayment rate), Weighted average 11.59% [2],[4]
Minimum [Member]
  
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]  
Expected size of losses, Range 9.73% [1],[5]
Current subordination levels, Range 0.00% [3],[5]
Prepayment speed (annual constant prepayment rate), Range 0.00% [4],[5]
Maximum [Member]
  
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]  
Expected size of losses, Range 100.00% [1],[5]
Current subordination levels, Range 0.00% [3],[5]
Prepayment speed (annual constant prepayment rate), Range 49.60% [4],[5]
[1] Represents future expected credit losses on impaired assets expressed as a percentage of total outstanding balance.
[2] Calculated by weighting the relevant input/assumption for each individual security by the outstanding notional of the security.
[3] Represents current level of credit protection (subordination) for the securities, expressed as a percentage of the balance of the collateral group backing the bond.
[4] Values represent high and low points of lifetime vectors of constant prepayment rates.
[5] Represents the range of inputs/assumptions based upon the individual securities within each category.