VARIABLE INTEREST ENTITIES, Not the Primary Beneficiary - Aggregate Assets, Liabilities Exposure to Loss (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Private Equity Interests
Variable interest entity, nonconsolidated, carrying amount of assets and liabilities [Abstract]
Aggregate assets	$ 5,175	$ 6,317
Aggregate liabilities	128	117
Our risk of loss	59	63
LIHTC funds
Variable interest entity, nonconsolidated, carrying amount of assets and liabilities [Abstract]
Aggregate assets	6,500	6,001
Aggregate liabilities	2,041	2,221
Our risk of loss	40	64
Other
Variable interest entity, nonconsolidated, carrying amount of assets and liabilities [Abstract]
Aggregate assets	220	205
Aggregate liabilities	129	115
Our risk of loss	4	4
Total VIEs - not primary beneficiary
Variable interest entity, nonconsolidated, carrying amount of assets and liabilities [Abstract]
Aggregate assets	11,895	12,523
Aggregate liabilities	2,298	2,453
Our risk of loss	$ 103	$ 131