AVAILABLE-FOR-SALE SECURITIES, Gross Unrealized Losses and Fair Value and Significant Assumptions (Details) - Bank - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	$ 4,066	$ 5,156
Unrealized losses less than 12 months	(245)	(405)
Estimated fair value 12 months or more	5,602	4,716
Unrealized losses 12 months or more	(885)	(810)
Total estimated fair value	9,668	9,872
Total unrealized losses	(1,130)	(1,215)
Agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	1,322	2,165
Unrealized losses less than 12 months	(99)	(226)
Estimated fair value 12 months or more	3,516	2,829
Unrealized losses 12 months or more	(489)	(442)
Total estimated fair value	4,838	4,994
Total unrealized losses	(588)	(668)
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	322	494
Unrealized losses less than 12 months	(21)	(41)
Estimated fair value 12 months or more	963	816
Unrealized losses 12 months or more	(178)	(167)
Total estimated fair value	1,285	1,310
Total unrealized losses	(199)	(208)
Agency CMOs
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	247	337
Unrealized losses less than 12 months	(24)	(32)
Estimated fair value 12 months or more	1,098	1,067
Unrealized losses 12 months or more	(216)	(201)
Total estimated fair value	1,345	1,404
Total unrealized losses	(240)	(233)
Other agency obligations
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	615	582
Unrealized losses less than 12 months	(28)	(31)
Estimated fair value 12 months or more	19	0
Unrealized losses 12 months or more	(1)	0
Total estimated fair value	634	582
Total unrealized losses	(29)	(31)
Non-agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	454	451
Unrealized losses less than 12 months	(41)	(41)
Estimated fair value 12 months or more	0	0
Unrealized losses 12 months or more	0	0
Total estimated fair value	454	451
Total unrealized losses	(41)	(41)
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	981	982
Unrealized losses less than 12 months	(28)	(28)
Estimated fair value 12 months or more	6	4
Unrealized losses 12 months or more	(1)	0
Total estimated fair value	987	986
Total unrealized losses	(29)	(28)
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	107	128
Unrealized losses less than 12 months	(4)	(5)
Estimated fair value 12 months or more	0	0
Unrealized losses 12 months or more	0	0
Total estimated fair value	107	128
Total unrealized losses	(4)	(5)
Other
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	18	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	18	17
Total unrealized losses	$ 0	$ (1)