Debt And Equity Securities (Summary Of Primary Assumptions Used In Estimating Cash Flows Expected To Be Collected For Securities) (Detail)	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Prepayment speeds, Range	9.90%
Default rates, Range	3.30%
Loss severity, Range	22.80%
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Prepayment speeds, Range	8.50%
Default rates, Range	1.60%
Loss severity, Range	3.30%
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Prepayment speeds, Range	11.20%
Default rates, Range	6.80%
Loss severity, Range	35.80%