COLLATERALIZED AGREEMENTS AND FINANCINGS, Repurchase Agreements, Securities Lending Transactions & Repurchase-to-Maturity Transactions Accounted for as Secured Borrowings (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	$ 205	$ 165
Total collateralized financings	277	250
Government and agency obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	122	87
Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	83	78
Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	72	85
Overnight and continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	205	165
Total collateralized financings	277	250
Overnight and continuous | Government and agency obligations
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	122	87
Overnight and continuous | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	83	78
Overnight and continuous | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	72	85
Up to 30 days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	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]
Repurchase agreements	0	0
Up to 30 days | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	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]
Repurchase agreements	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]
Repurchase agreements	0	0
30-90 days | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	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]
Repurchase agreements	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]
Repurchase agreements	0	0
Greater than 90 days | Agency MBS and agency CMOs
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Repurchase agreements	0	0
Greater than 90 days | Equity securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Equity securities	$ 0	$ 0