COLLATERALIZED AGREEMENTS AND FINANCINGS, Repurchase Agreements, Securities Lending Transactions & Repurchase-to-Maturity Transactions Accounted for as Secured Borrowings (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	$ 165	$ 150
Total collateralized financings	250	473
Government and agency obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	87	70
Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	78	80
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	85	323
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	165	150
Total collateralized financings	250	473
Overnight and continuous | Government and agency obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	87	70
Overnight and continuous | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	78	80
Overnight and continuous | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	85	323
Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
Total collateralized financings	0	0
Up to 30 days | Government and agency obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
Up to 30 days | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
Up to 30 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	0	0
30-90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
Total collateralized financings	0	0
30-90 days | Government and agency obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
30-90 days | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
30-90 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	0	0
Greater than 90 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
Total collateralized financings	0	0
Greater than 90 days | Government and agency obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
Greater than 90 days | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Financial assets sold under agreements to repurchase	0	0
Greater than 90 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	$ 0	$ 0