AVAILABLE-FOR-SALE SECURITIES, Contractual Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Sep. 30, 2025
Amortized cost
Within one year	$ 649
After one but within five years	1,384
After five but within ten years	1,738
After ten years	3,343
Cost basis	7,114	$ 7,410
Fair value
Within one year	647
After one but within five years	1,307
After five but within ten years	1,618
After ten years	3,076
Total	$ 6,648	6,888
Weighted-average yield
Within one year	2.92%
After one but within five years	1.75%
After five but within ten years	1.37%
After ten years	2.77%
Total	2.25%
Agency residential MBS
Amortized cost
Within one year	$ 1
After one but within five years	290
After five but within ten years	1,641
After ten years	1,480
Cost basis	3,412	3,531
Fair value
Within one year	1
After one but within five years	277
After five but within ten years	1,522
After ten years	1,380
Total	$ 3,180	3,269
Weighted-average yield
Within one year	2.06%
After one but within five years	1.29%
After five but within ten years	1.31%
After ten years	2.79%
Total	1.95%
Agency commercial MBS
Amortized cost
Within one year	$ 250
After one but within five years	853
After five but within ten years	16
After ten years	45
Cost basis	1,164	1,223
Fair value
Within one year	247
After one but within five years	789
After five but within ten years	15
After ten years	38
Total	$ 1,089	1,138
Weighted-average yield
Within one year	1.47%
After one but within five years	1.29%
After five but within ten years	1.25%
After ten years	1.85%
Total	1.35%
Agency CMOs
Amortized cost
Within one year	$ 0
After one but within five years	0
After five but within ten years	32
After ten years	1,336
Cost basis	1,368	1,421
Fair value
Within one year	0
After one but within five years	0
After five but within ten years	30
After ten years	1,205
Total	$ 1,235	1,277
Weighted-average yield
Within one year	0.00%
After one but within five years	0.00%
After five but within ten years	1.46%
After ten years	2.32%
Total	2.30%
U.S. Treasuries
Amortized cost
Within one year	$ 338
After one but within five years	90
After five but within ten years	0
After ten years	0
Cost basis	428	429
Fair value
Within one year	339
After one but within five years	90
After five but within ten years	0
After ten years	0
Total	$ 429	430
Weighted-average yield
Within one year	3.92%
After one but within five years	3.83%
After five but within ten years	0.00%
After ten years	0.00%
Total	3.90%
Other agency obligations
Amortized cost
Within one year	$ 53
After one but within five years	104
After five but within ten years	28
After ten years	8
Cost basis	193	229
Fair value
Within one year	53
After one but within five years	104
After five but within ten years	28
After ten years	7
Total	$ 192	227
Weighted-average yield
Within one year	2.91%
After one but within five years	3.63%
After five but within ten years	2.42%
After ten years	3.07%
Total	3.23%
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	464
Cost basis	464	484
Fair value
Within one year	0
After one but within five years	0
After five but within ten years	0
After ten years	436
Total	$ 436	453
Weighted-average yield
Within one year	0.00%
After one but within five years	0.00%
After five but within ten years	0.00%
After ten years	4.07%
Total	4.07%
Corporate bonds
Amortized cost
Within one year	$ 7
After one but within five years	47
After five but within ten years	17
After ten years	0
Cost basis	71	79
Fair value
Within one year	7
After one but within five years	47
After five but within ten years	18
After ten years	0
Total	$ 72	79
Weighted-average yield
Within one year	6.34%
After one but within five years	4.82%
After five but within ten years	5.03%
After ten years	0.00%
Total	5.02%
All other investments
Amortized cost
Within one year	$ 0
After one but within five years	0
After five but within ten years	4
After ten years	10
Cost basis	14	14
Fair value
Within one year	0
After one but within five years	0
After five but within ten years	5
After ten years	10
Total	$ 15	$ 15
Weighted-average yield
Within one year	0.00%
After one but within five years	0.00%
After five but within ten years	6.85%
After ten years	6.46%
Total	6.59%