AVAILABLE-FOR-SALE SECURITIES, Contractual Maturities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Carrying value
Total	$ 9,566	$ 9,885
Bank
Amortized cost
Within one year	502
After one but within five years	2,556
After five but within ten years	2,897
After ten years	4,717
Cost basis	10,672	11,100
Carrying value
Within one year	492
After one but within five years	2,412
After five but within ten years	2,561
After ten years	4,101
Total	$ 9,566	9,885
Weighted-average yield
Within one year (in hundredths)	2.54%
After one but within five years (in hundredths)	2.81%
After five but within ten years (in hundredths)	1.38%
After ten years (in hundredths)	2.05%
Total (in hundredths)	2.07%
Bank | Agency residential MBS
Amortized cost
Within one year	$ 0
After one but within five years	127
After five but within ten years	2,240
After ten years	2,697
Cost basis	5,064	5,662
Carrying value
Within one year	0
After one but within five years	122
After five but within ten years	2,011
After ten years	2,372
Total	$ 4,505	4,994
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	2.46%
After five but within ten years (in hundredths)	1.29%
After ten years (in hundredths)	1.90%
Total (in hundredths)	1.65%
Bank | Agency commercial MBS
Amortized cost
Within one year	$ 0
After one but within five years	919
After five but within ten years	499
After ten years	51
Cost basis	1,469	1,518
Carrying value
Within one year	0
After one but within five years	824
After five but within ten years	406
After ten years	42
Total	$ 1,272	1,310
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	1.61%
After five but within ten years (in hundredths)	1.21%
After ten years (in hundredths)	1.87%
Total (in hundredths)	1.48%
Bank | Agency CMOs
Amortized cost
Within one year	$ 0
After one but within five years	10
After five but within ten years	45
After ten years	1,442
Cost basis	1,497	1,637
Carrying value
Within one year	0
After one but within five years	8
After five but within ten years	40
After ten years	1,204
Total	$ 1,252	1,404
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	2.27%
After five but within ten years (in hundredths)	1.54%
After ten years (in hundredths)	1.57%
Total (in hundredths)	1.58%
Bank | Other agency obligations
Amortized cost
Within one year	$ 60
After one but within five years	560
After five but within ten years	80
After ten years	10
Cost basis	710	613
Carrying value
Within one year	59
After one but within five years	539
After five but within ten years	74
After ten years	10
Total	$ 682	582
Weighted-average yield
Within one year (in hundredths)	2.54%
After one but within five years (in hundredths)	3.24%
After five but within ten years (in hundredths)	3.44%
After ten years (in hundredths)	3.07%
Total (in hundredths)	3.20%
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	509
Cost basis	509	492
Carrying value
Within one year	0
After one but within five years	0
After five but within ten years	0
After ten years	465
Total	$ 465	451
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	0.00%
After five but within ten years (in hundredths)	0.00%
After ten years (in hundredths)	4.10%
Total (in hundredths)	4.10%
Bank | U.S. Treasuries
Amortized cost
Within one year	$ 417
After one but within five years	848
After five but within ten years	0
After ten years	0
Cost basis	1,265	1,014
Carrying value
Within one year	408
After one but within five years	830
After five but within ten years	0
After ten years	0
Total	$ 1,238	986
Weighted-average yield
Within one year (in hundredths)	2.40%
After one but within five years (in hundredths)	3.51%
After five but within ten years (in hundredths)	0.00%
After ten years (in hundredths)	0.00%
Total (in hundredths)	3.14%
Bank | Corporate bonds
Amortized cost
Within one year	$ 25
After one but within five years	87
After five but within ten years	28
After ten years	0
Cost basis	140	146
Carrying value
Within one year	25
After one but within five years	84
After five but within ten years	25
After ten years	0
Total	$ 134	141
Weighted-average yield
Within one year (in hundredths)	4.79%
After one but within five years (in hundredths)	6.32%
After five but within ten years (in hundredths)	4.90%
After ten years (in hundredths)	0.00%
Total (in hundredths)	5.76%
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	8
Cost basis	18	18
Carrying value
Within one year	0
After one but within five years	5
After five but within ten years	5
After ten years	8
Total	$ 18	$ 17
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	7.05%
After five but within ten years (in hundredths)	5.23%
After ten years (in hundredths)	8.05%
Total (in hundredths)	7.06%