AVAILABLE-FOR-SALE SECURITIES, Gross Unrealized Losses and Fair Value and Significant Assumptions (Details) - Bank - USD ($) $ in Millions	Jun. 30, 2022	Sep. 30, 2021
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	$ 7,728	$ 4,721
Unrealized losses less than 12 months	(427)	(50)
Estimated fair value 12 months or more	2,345	602
Unrealized losses 12 months or more	(300)	(19)
Total estimated fair value	10,073	5,323
Total unrealized losses	(727)	(69)
Agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	4,288	3,155
Unrealized losses less than 12 months	(267)	(25)
Estimated fair value 12 months or more	1,149	18
Unrealized losses 12 months or more	(123)	0
Total estimated fair value	5,437	3,173
Total unrealized losses	(390)	(25)
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	607	645
Unrealized losses less than 12 months	(44)	(13)
Estimated fair value 12 months or more	649	353
Unrealized losses 12 months or more	(100)	(15)
Total estimated fair value	1,256	998
Total unrealized losses	(144)	(28)
Agency CMOs
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	961	918
Unrealized losses less than 12 months	(85)	(12)
Estimated fair value 12 months or more	547	231
Unrealized losses 12 months or more	(76)	(4)
Total estimated fair value	1,508	1,149
Total unrealized losses	(161)	(16)
Other agency obligations
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	487
Unrealized losses less than 12 months	(11)
Estimated fair value 12 months or more	0
Unrealized losses 12 months or more	0
Total estimated fair value	487
Total unrealized losses	(11)
Non-agency residential MBS
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	471
Unrealized losses less than 12 months	(11)
Estimated fair value 12 months or more	0
Unrealized losses 12 months or more	0
Total estimated fair value	471
Total unrealized losses	(11)
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	776	3
Unrealized losses less than 12 months	(7)	0
Estimated fair value 12 months or more	0	0
Unrealized losses 12 months or more	0	0
Total estimated fair value	776	3
Total unrealized losses	(7)	$ 0
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	120
Unrealized losses less than 12 months	(1)
Estimated fair value 12 months or more	0
Unrealized losses 12 months or more	0
Total estimated fair value	120
Total unrealized losses	(1)
Other
Debt Securities, Available-for-sale [Line Items]
Estimated far value less than 12 months	18
Unrealized losses less than 12 months	(1)
Estimated fair value 12 months or more	0
Unrealized losses 12 months or more	(1)
Total estimated fair value	18
Total unrealized losses	$ (2)