BANK DEPOSITS, Schedule Maturities of Certificates of Deposit (Details) - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021
Scheduled maturities of certificates of deposit, denominations greater than or equal to $100,000 [Abstract]
Three months or less	$ 50	$ 22
Over three through six months	20	21
Over six through twelve months	35	32
Over one through two years	69	93
Over two through three years	7	37
Over three through four years	8	6
Over four through five years	9	9
Total certificates of deposit	198	220
Scheduled maturities of certificates of deposit, denominations less than 100,000 [Abstract]
Three months or less	30	87
Over three through six months	27	76
Over six through twelve months	112	54
Over one through two years	172	170
Over two through three years	151	166
Over three through four years	5	99
Over four through five years	6	6
Total certificates of deposit	$ 503	$ 658