Investments (Significant Inputs Used In Measurement Of Credit Losses On Securities) (Detail)	3 Months Ended
	Mar. 31, 2012
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Expected size of losses, Weighted average	90.60%	[1],[2]
Current subordination levels, Weighted average	0.00%	[2],[3]
Prepayment speed (annual constant prepayment rate), Weighted average	10.21%	[2],[4]
Minimum [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Expected size of losses, Range	12.13%	[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	22.68%	[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.