VARIABLE INTEREST ENTITIES, Not the Primary Beneficiary - Aggregate Assets, Liabilities Exposure to Loss (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023
Variable Interest Entity [Line Items]
Aggregate assets	$ 80,130	$ 78,360
Aggregate liabilities	69,349	68,173
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Aggregate assets	11,747	11,243
Aggregate liabilities	3,967	3,703
Our risk of loss	151	217
Variable Interest Entity, Not Primary Beneficiary | LIHTC
Variable Interest Entity [Line Items]
Aggregate assets	8,854	8,451
Aggregate liabilities	3,146	2,964
Our risk of loss	47	113
Variable Interest Entity, Not Primary Beneficiary | Private Equity Interests
Variable Interest Entity [Line Items]
Aggregate assets	2,709	2,591
Aggregate liabilities	752	655
Our risk of loss	101	101
Variable Interest Entity, Not Primary Beneficiary | Other
Variable Interest Entity [Line Items]
Aggregate assets	184	201
Aggregate liabilities	69	84
Our risk of loss	$ 3	$ 3