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NON-CONSOLIDATED VARIABLE INTEREST ENTITIES AND SERVICING ASSETS - Key Economic Assumptions Used in Determining Fair Value at Time of Sale of Loans (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Government Guaranteed Mortgage Loans [Member] | Maximum [Member]      
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities [Line Items]      
Constant prepayment rate 6.20% 7.60% 9.20%
Discount rate 12.00% 12.00% 11.50%
Government Guaranteed Mortgage Loans [Member] | Minimum [Member]      
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities [Line Items]      
Constant prepayment rate 6.00% 5.90% 7.80%
Discount rate 12.00% 11.50% 11.50%
Conventional Loan [Member] | Maximum [Member]      
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities [Line Items]      
Constant prepayment rate 6.70% 8.00% 9.00%
Discount rate 10.00% 10.00% 9.50%
Conventional Loan [Member] | Minimum [Member]      
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities [Line Items]      
Constant prepayment rate 6.30% 6.30% 7.90%
Discount rate 10.00% 9.50% 9.50%
Conventional Non Conforming Mortgage Loans [Member] | Maximum [Member]      
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities [Line Items]      
Constant prepayment rate 9.50% 14.10% 14.40%
Discount rate 14.30% 14.30% 13.80%
Conventional Non Conforming Mortgage Loans [Member] | Minimum [Member]      
Assumption For Fair Value On Securitization Date Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities [Line Items]      
Constant prepayment rate 9.10% 9.30% 12.90%
Discount rate 14.30% 13.80% 13.80%