VARIABLE INTEREST ENTITIES, Primary Beneficiary - Aggregate Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	$ 53,657	$ 47,482
Total liabilities	46,219	40,306
Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	234	221
Total liabilities	93	94
Private Equity Interests [Member] | Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	48	39
Total liabilities	4	4
LIHTC Funds [Member] | Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	165	168
Total liabilities	68	76
Restricted Stock Trust Fund [Member] | Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	21	14
Total liabilities	$ 21	$ 14