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FAIR VALUE MEASUREMENTS - Information about Significant Unobservable Inputs Used for Recurring Fair Value Measurements for Level 3 MSRs (Detail) - Fair Value, Measurements, Recurring - Level 3	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service	$ 92
Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service	103
Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service	98
Interest in MSRs | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service	78
Interest in MSRs | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service	84
Interest in MSRs | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service	$ 81
Consolidated VIEs | Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service		$ 83
Consolidated VIEs | Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service		108
Consolidated VIEs | Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
Cost to service		$ 98
Discount rate | Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.030
Discount rate | Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.126
Discount rate | Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.077
Discount rate | Interest in MSRs | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.075
Discount rate | Interest in MSRs | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.090
Discount rate | Interest in MSRs | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.079
Discount rate | Consolidated VIEs | Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.090
Discount rate | Consolidated VIEs | Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.120
Discount rate | Consolidated VIEs | Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.094
Prepayment rate | Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.069
Prepayment rate | Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.178
Prepayment rate | Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.090
Prepayment rate | Interest in MSRs | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.051
Prepayment rate | Interest in MSRs | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.159
Prepayment rate | Interest in MSRs | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.096
Prepayment rate | Consolidated VIEs | Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.193
Prepayment rate | Consolidated VIEs | Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.555
Prepayment rate | Consolidated VIEs | Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.420
Delinquency rate | Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.009
Delinquency rate | Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.014
Delinquency rate | Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.010
Delinquency rate | Interest in MSRs | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.000
Delinquency rate | Interest in MSRs | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.002
Delinquency rate | Interest in MSRs | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs	0.001
Delinquency rate | Consolidated VIEs | Mortgage Servicing Rights | Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.000
Delinquency rate | Consolidated VIEs | Mortgage Servicing Rights | Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.060
Delinquency rate | Consolidated VIEs | Mortgage Servicing Rights | Weighted Average
Fair Value, Option, Quantitative Disclosures [Line Items]
MSR measurement inputs		0.025

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Value of input used to measure servicing asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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