INVESTMENT SECURITIES - Roll-Forward of Credit Losses on Debt Securities Held by Corporation (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Beginning balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	$ 28,981	$ 19,030	$ 22,294	$ 5,777
Additions:
Credit losses on debt securities for which an OTTI was no previously recognized	0	0	0	12,856
Credit losses on debt securities for which an OTTI was previously recognized	0	231	6,687	628
Reductions:
Ending balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	28,981	19,261	28,981	19,261
Mortgage Backed Securities Issued By Private Enterprises [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Beginning balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	6,792	6,174	6,405	5,777
Additions:
Credit losses on debt securities for which an OTTI was no previously recognized		0	0	0
Credit losses on debt securities for which an OTTI was previously recognized	0	231	387	628
Reductions:
Ending balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	6,792	6,405	6,792	6,405
US States And Political Subdivisions Member [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Beginning balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	22,189	12,856	15,889	0
Additions:
Credit losses on debt securities for which an OTTI was no previously recognized	0	0	0	12,856
Credit losses on debt securities for which an OTTI was previously recognized	0	0	6,300	0
Reductions:
Ending balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	$ 22,189	$ 12,856	$ 22,189	$ 12,856