COMMITMENTS, CONTINGENCIES AND GUARANTEES, Commitments and Contingencies (Details) $ in Millions	9 Months Ended
	Jun. 30, 2020 USD ($) agreements
Independent venture capital or private equity investment commitment
Commitments [Line Items]
Amount of commitment	$ 38
Commitment to lend to RJTCF
Commitments [Line Items]
Amount of commitment	$ 130
Number of days that investments in project partnerships typically sold	90 days
Forward GNMA MBS purchase commitments
Commitments [Line Items]
Amount of commitment	$ 426
Expected time of purchase (in days)	90 days
Underwriting commitment
Commitments [Line Items]
Number of open underwriting commitments | agreements	11