AVAILABLE-FOR-SALE SECURITIES, Gross Unrealized Losses and Fair Value and Significant Assumptions (Details) - Bank - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	$ 515	$ 373
Unrealized losses, less than 12 months	0	(5)
Fair value, 12 months or more	7,311	8,617
Unrealized losses, 12 months or more	(653)	(1,247)
Fair value	7,826	8,990
Unrealized losses	(653)	(1,252)
Agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0	73
Unrealized losses, less than 12 months	0	(3)
Fair value, 12 months or more	3,679	4,119
Unrealized losses, 12 months or more	(327)	(651)
Fair value	3,679	4,192
Unrealized losses	(327)	(654)
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0	3
Unrealized losses, less than 12 months	0	0
Fair value, 12 months or more	1,287	1,250
Unrealized losses, 12 months or more	(119)	(211)
Fair value	1,287	1,253
Unrealized losses	(119)	(211)
Agency CMOs
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	30	0
Unrealized losses, less than 12 months	0	0
Fair value, 12 months or more	1,114	1,183
Unrealized losses, 12 months or more	(170)	(265)
Fair value	1,144	1,183
Unrealized losses	(170)	(265)
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	475	120
Unrealized losses, less than 12 months	0	0
Fair value, 12 months or more	229	995
Unrealized losses, 12 months or more	(2)	(21)
Fair value	704	1,115
Unrealized losses	(2)	(21)
Other agency obligations
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	10	97
Unrealized losses, less than 12 months	0	(1)
Fair value, 12 months or more	539	582
Unrealized losses, 12 months or more	(6)	(30)
Fair value	549	679
Unrealized losses	(6)	(31)
Non-agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0	62
Unrealized losses, less than 12 months	0	(1)
Fair value, 12 months or more	417	401
Unrealized losses, 12 months or more	(27)	(63)
Fair value	417	463
Unrealized losses	(27)	(64)
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0	13
Unrealized losses, less than 12 months	0	0
Fair value, 12 months or more	42	78
Unrealized losses, 12 months or more	(2)	(6)
Fair value	42	91
Unrealized losses	(2)	(6)
Other
Debt Securities, Available-for-sale [Line Items]
Fair value, less than 12 months	0	5
Unrealized losses, less than 12 months	0	0
Fair value, 12 months or more	4	9
Unrealized losses, 12 months or more	0	0
Fair value	4	14
Unrealized losses	$ 0	$ 0