AVAILABLE-FOR-SALE SECURITIES, Gross Unrealized Losses and Fair Value and Significant Assumptions (Details) - Bank - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	$ 969	$ 5,156
Unrealized losses less than 12 months	(26)	(405)
Estimated fair value 12 months or more	8,363	4,716
Unrealized losses 12 months or more	(1,081)	(810)
Total estimated fair value	9,332	9,872
Total unrealized losses	(1,107)	(1,215)
Agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	190	2,165
Unrealized losses less than 12 months	(8)	(226)
Estimated fair value 12 months or more	4,274	2,829
Unrealized losses 12 months or more	(552)	(442)
Total estimated fair value	4,464	4,994
Total unrealized losses	(560)	(668)
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	136	494
Unrealized losses less than 12 months	(5)	(41)
Estimated fair value 12 months or more	1,136	816
Unrealized losses 12 months or more	(192)	(167)
Total estimated fair value	1,272	1,310
Total unrealized losses	(197)	(208)
Agency CMOs
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	26	337
Unrealized losses less than 12 months	(1)	(32)
Estimated fair value 12 months or more	1,226	1,067
Unrealized losses 12 months or more	(244)	(201)
Total estimated fair value	1,252	1,404
Total unrealized losses	(245)	(233)
Other agency obligations
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	208	582
Unrealized losses less than 12 months	(3)	(31)
Estimated fair value 12 months or more	474	0
Unrealized losses 12 months or more	(25)	0
Total estimated fair value	682	582
Total unrealized losses	(28)	(31)
Non-agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	53	451
Unrealized losses less than 12 months	(2)	(41)
Estimated fair value 12 months or more	412	0
Unrealized losses 12 months or more	(42)	0
Total estimated fair value	465	451
Total unrealized losses	(44)	(41)
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	325	982
Unrealized losses less than 12 months	(6)	(28)
Estimated fair value 12 months or more	763	4
Unrealized losses 12 months or more	(21)	0
Total estimated fair value	1,088	986
Total unrealized losses	(27)	(28)
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	26	128
Unrealized losses less than 12 months	(1)	(5)
Estimated fair value 12 months or more	65	0
Unrealized losses 12 months or more	(5)	0
Total estimated fair value	91	128
Total unrealized losses	(6)	(5)
Other
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	5	17
Unrealized losses less than 12 months	0	(1)
Estimated fair value 12 months or more	13	0
Unrealized losses 12 months or more	0	0
Total estimated fair value	18	17
Total unrealized losses	$ 0	$ (1)