Investment Securities (Significant Assumptions of Other-Than-Temporarily Impaired Securities) (Detail)	6 Months Ended
	Jun. 30, 2013
Disclosure Investment Securities Significant Assumptions Of Other Than Temporarily Impaired Securities [Abstract]
Conditional repayment rate	10.40%	[1]
Loss severity	42.00%	[2]
Conditional default rate	3.60%	[3]

[1] Conditional repayment rate represents a rate equal to the proportion of principal balance paid off voluntarily over a certain period of time on an annualized basis.

[2] Loss severity rates are projected by considering collateral characteristics such as current loan-to-value, original creditworthiness of borrowers (FICO score) and geographic concentration.

[3] Conditional default rate is an annualized rate of default on a group of mortgages, and represents the percentage of outstanding principal balances in the pool that are in default, which typically equates to the borrower being past due 60 days, 90 days, or possibly already in the foreclosure process.