AVAILABLE-FOR-SALE SECURITIES, Contractual Maturities (Details) - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023
Fair value
Total	$ 8,530	$ 9,181
Bank
Amortized cost
Within one year	1,040
After one but within five years	1,668
After five but within ten years	2,323
After ten years	4,413
Cost basis	9,444	10,433
Fair value
Within one year	1,032
After one but within five years	1,576
After five but within ten years	2,078
After ten years	3,844
Total	$ 8,530	9,181
Weighted-average yield
Within one year (as a percent)	3.45%
After one but within five years (as a percent)	2.69%
After five but within ten years (as a percent)	1.35%
After ten years (as a percent)	2.27%
Total (as a percent)	2.25%
Bank | Agency residential MBS
Amortized cost
Within one year	$ 1
After one but within five years	99
After five but within ten years	1,804
After ten years	2,440
Cost basis	4,344	4,865
Fair value
Within one year	1
After one but within five years	97
After five but within ten years	1,638
After ten years	2,137
Total	$ 3,873	4,211
Weighted-average yield
Within one year (as a percent)	1.85%
After one but within five years (as a percent)	2.52%
After five but within ten years (as a percent)	1.29%
After ten years (as a percent)	2.04%
Total (as a percent)	1.74%
Bank | Agency commercial MBS
Amortized cost
Within one year	$ 67
After one but within five years	911
After five but within ten years	412
After ten years	49
Cost basis	1,439	1,464
Fair value
Within one year	66
After one but within five years	833
After five but within ten years	342
After ten years	39
Total	$ 1,280	1,253
Weighted-average yield
Within one year (as a percent)	3.04%
After one but within five years (as a percent)	1.53%
After five but within ten years (as a percent)	1.17%
After ten years (as a percent)	1.87%
Total (as a percent)	1.51%
Bank | Agency CMOs
Amortized cost
Within one year	$ 0
After one but within five years	6
After five but within ten years	36
After ten years	1,339
Cost basis	1,381	1,448
Fair value
Within one year	0
After one but within five years	6
After five but within ten years	32
After ten years	1,129
Total	$ 1,167	1,183
Weighted-average yield
Within one year (as a percent)	0.00%
After one but within five years (as a percent)	2.34%
After five but within ten years (as a percent)	1.52%
After ten years (as a percent)	1.73%
Total (as a percent)	1.73%
Bank | Other agency obligations
Amortized cost
Within one year	$ 195
After one but within five years	382
After five but within ten years	43
After ten years	9
Cost basis	629	710
Fair value
Within one year	192
After one but within five years	372
After five but within ten years	40
After ten years	9
Total	$ 613	679
Weighted-average yield
Within one year (as a percent)	2.64%
After one but within five years (as a percent)	3.59%
After five but within ten years (as a percent)	3.05%
After ten years (as a percent)	3.07%
Total (as a percent)	3.25%
Bank | Non-agency residential MBS
Amortized cost
Within one year	$ 0
After one but within five years	0
After five but within ten years	0
After ten years	567
Cost basis	567	527
Fair value
Within one year	0
After one but within five years	0
After five but within ten years	0
After ten years	521
Total	$ 521	463
Weighted-average yield
Within one year (as a percent)	0.00%
After one but within five years (as a percent)	0.00%
After five but within ten years (as a percent)	0.00%
After ten years (as a percent)	4.39%
Total (as a percent)	4.39%
Bank | U.S. Treasuries
Amortized cost
Within one year	$ 763
After one but within five years	186
After five but within ten years	0
After ten years	0
Cost basis	949	1,261
Fair value
Within one year	759
After one but within five years	186
After five but within ten years	0
After ten years	0
Total	$ 945	1,240
Weighted-average yield
Within one year (as a percent)	3.68%
After one but within five years (as a percent)	5.23%
After five but within ten years (as a percent)	0.00%
After ten years (as a percent)	0.00%
Total (as a percent)	3.99%
Bank | Corporate bonds
Amortized cost
Within one year	$ 14
After one but within five years	79
After five but within ten years	23
After ten years	0
Cost basis	116	140
Fair value
Within one year	14
After one but within five years	77
After five but within ten years	22
After ten years	0
Total	$ 113	134
Weighted-average yield
Within one year (as a percent)	3.71%
After one but within five years (as a percent)	5.78%
After five but within ten years (as a percent)	5.02%
After ten years (as a percent)	0.00%
Total (as a percent)	5.38%
Bank | Other
Amortized cost
Within one year	$ 0
After one but within five years	5
After five but within ten years	5
After ten years	9
Cost basis	19	18
Fair value
Within one year	0
After one but within five years	5
After five but within ten years	4
After ten years	9
Total	$ 18	$ 18
Weighted-average yield
Within one year (as a percent)	0.00%
After one but within five years (as a percent)	7.38%
After five but within ten years (as a percent)	5.21%
After ten years (as a percent)	8.24%
Total (as a percent)	7.21%