VARIABLE INTEREST ENTITIES, Primary Beneficiary - Aggregate Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	$ 56,066	$ 47,482
Total liabilities	48,429	40,306
Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	137	221
Total liabilities	31	94
Private Equity Interests | Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	48	39
Total liabilities	4	4
LIHTC funds | Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	68	168
Total liabilities	6	76
Restricted Stock Trust Fund | Variable Interest Entity, Primary Beneficiary
Variable interest entity, consolidated, aggregate assets and liabilities [Abstract]
Total assets	21	14
Total liabilities	$ 21	$ 14