Impairment of Investment Securities - Cumulative Roll Forward of Credit Losses Recognized in Earnings for Debt Securities Held and Not Intended to be Sold (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Impairment of Investment Securities Disclosure [Abstract]
Balance, beginning (a)	$ 26,842	$ 42,699	$ 27,543	[1]	$ 43,274	[1]
Credit losses on debt securities for which other-than-temporary impairment was not previously recognized	0	0	0		0
Additional credit losses on debt securities for which other-than-temporary impairment was previously recognized	0	0	0		0
Balance, ending	26,554	41,373	26,554		41,373
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Cash Flows	$ (288)	$ (1,326)	$ (989)		$ (1,901)

[1] The beginning balance represents credit related losses included in other-than-temporary impairment charges recognized on debt securities in prior periods.