AVAILABLE-FOR-SALE SECURITIES, Gross Unrealized Losses and Fair Value and Significant Assumptions (Details) - Bank - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	$ 2,600	$ 5,156
Unrealized losses less than 12 months	(116)	(405)
Estimated fair value 12 months or more	7,007	4,716
Unrealized losses 12 months or more	(889)	(810)
Total estimated fair value	9,607	9,872
Total unrealized losses	(1,005)	(1,215)
Agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	673	2,165
Unrealized losses less than 12 months	(40)	(226)
Estimated fair value 12 months or more	4,018	2,829
Unrealized losses 12 months or more	(480)	(442)
Total estimated fair value	4,691	4,994
Total unrealized losses	(520)	(668)
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	145	494
Unrealized losses less than 12 months	(4)	(41)
Estimated fair value 12 months or more	1,154	816
Unrealized losses 12 months or more	(174)	(167)
Total estimated fair value	1,299	1,310
Total unrealized losses	(178)	(208)
Agency CMOs
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	40	337
Unrealized losses less than 12 months	(1)	(32)
Estimated fair value 12 months or more	1,287	1,067
Unrealized losses 12 months or more	(217)	(201)
Total estimated fair value	1,327	1,404
Total unrealized losses	(218)	(233)
Other agency obligations
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	386	582
Unrealized losses less than 12 months	(11)	(31)
Estimated fair value 12 months or more	301	0
Unrealized losses 12 months or more	(12)	0
Total estimated fair value	687	582
Total unrealized losses	(23)	(31)
Non-agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	469	451
Unrealized losses less than 12 months	(39)	(41)
Estimated fair value 12 months or more	0	0
Unrealized losses 12 months or more	0	0
Total estimated fair value	469	451
Total unrealized losses	(39)	(41)
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	749	982
Unrealized losses less than 12 months	(16)	(28)
Estimated fair value 12 months or more	247	4
Unrealized losses 12 months or more	(6)	0
Total estimated fair value	996	986
Total unrealized losses	(22)	(28)
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	125	128
Unrealized losses less than 12 months	(5)	(5)
Estimated fair value 12 months or more	0	0
Unrealized losses 12 months or more	0	0
Total estimated fair value	125	128
Total unrealized losses	(5)	(5)
Other
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	13	17
Unrealized losses less than 12 months	0	(1)
Estimated fair value 12 months or more	0	0
Unrealized losses 12 months or more	0	0
Total estimated fair value	13	17
Total unrealized losses	$ 0	$ (1)