BANK DEPOSITS, Schedule Maturities of Certificates of Deposit (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Scheduled maturities of certificates of deposit, denominations greater than or equal to $100,000 [Abstract]
Three months or less	$ 71	$ 24
Over three through six months	55	26
Over six through twelve months	28	75
Over one through two years	36	32
Over two through three years	58	40
Over three through four years	56	66
Over four through five years	7	38
Total certificates of deposit	311	301
Scheduled maturities of certificates of deposit, denominations less than 100,000 [Abstract]
Three months or less	30	19
Over three through six months	73	21
Over six through twelve months	22	37
Over one through two years	198	36
Over two through three years	149	93
Over three through four years	156	47
Over four through five years	149	51
Total certificates of deposit	$ 777	$ 304