BANK DEPOSITS, Schedule Maturities of Certificates of Deposit (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Scheduled maturities of certificates of deposit, denominations greater than or equal to $100,000 [Abstract]
Three months or less	$ 84	$ 24
Over three through six months	57	26
Over six through twelve months	67	75
Over one through two years	26	32
Over two through three years	54	40
Over three through four years	68	66
Over four through five years	7	38
Total certificates of deposit	363	301
Scheduled maturities of certificates of deposit, denominations less than 100,000 [Abstract]
Three months or less	20	19
Over three through six months	26	21
Over six through twelve months	85	37
Over one through two years	175	36
Over two through three years	160	93
Over three through four years	171	47
Over four through five years	150	51
Total certificates of deposit	$ 787	$ 304