COMMITMENTS, CONTINGENCIES AND GUARANTEES (Details) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($) agreement
Commitments [Line Items]
Amount of commitment	$ 15
Underwriting commitment
Commitments [Line Items]
Number of open underwriting commitments | agreement	6
Various Investment Commitment
Commitments [Line Items]
Amount of commitment	$ 36
Commitment to lend to RJTCF
Commitments [Line Items]
Amount of commitment	$ 56
Number of days that investments in project partnerships are typically sold (in days)	90 days
Forward GNMA MBS purchase commitments
Commitments [Line Items]
Amount of commitment	$ 443
Expected time of purchase (in days)	90 days