AVAILABLE-FOR-SALE SECURITIES, Contractual Maturities (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Carrying value
Total	$ 9,773	$ 9,885
Bank
Amortized cost
Within one year	227
After one but within five years	2,607
After five but within ten years	3,061
After ten years	4,882
Cost basis	10,777	11,100
Carrying value
Within one year	223
After one but within five years	2,485
After five but within ten years	2,746
After ten years	4,319
Total	$ 9,773	9,885
Weighted-average yield
Within one year (in hundredths)	2.27%
After one but within five years (in hundredths)	2.66%
After five but within ten years (in hundredths)	1.42%
After ten years (in hundredths)	2.06%
Total (in hundredths)	2.03%
Bank | Agency residential MBS
Amortized cost
Within one year	$ 0
After one but within five years	138
After five but within ten years	2,332
After ten years	2,802
Cost basis	5,272	5,662
Carrying value
Within one year	0
After one but within five years	134
After five but within ten years	2,120
After ten years	2,499
Total	$ 4,753	4,994
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	2.47%
After five but within ten years (in hundredths)	1.30%
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	876
After five but within ten years	550
After ten years	51
Cost basis	1,477	1,518
Carrying value
Within one year	0
After one but within five years	797
After five but within ten years	459
After ten years	43
Total	$ 1,299	1,310
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	1.63%
After five but within ten years (in hundredths)	1.25%
After ten years (in hundredths)	1.87%
Total (in hundredths)	1.50%
Bank | Agency CMOs
Amortized cost
Within one year	$ 0
After one but within five years	11
After five but within ten years	41
After ten years	1,493
Cost basis	1,545	1,637
Carrying value
Within one year	0
After one but within five years	10
After five but within ten years	37
After ten years	1,280
Total	$ 1,327	1,404
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	2.28%
After five but within ten years (in hundredths)	1.51%
After ten years (in hundredths)	1.61%
Total (in hundredths)	1.61%
Bank | Other agency obligations
Amortized cost
Within one year	$ 35
After one but within five years	609
After five but within ten years	105
After ten years	11
Cost basis	760	613
Carrying value
Within one year	34
After one but within five years	594
After five but within ten years	99
After ten years	10
Total	$ 737	582
Weighted-average yield
Within one year (in hundredths)	2.16%
After one but within five years (in hundredths)	3.42%
After five but within ten years (in hundredths)	3.58%
After ten years (in hundredths)	3.07%
Total (in hundredths)	3.38%
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	518
Cost basis	518	492
Carrying value
Within one year	0
After one but within five years	0
After five but within ten years	0
After ten years	479
Total	$ 479	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)	4.13%
Total (in hundredths)	4.13%
Bank | U.S. Treasuries
Amortized cost
Within one year	$ 191
After one but within five years	852
After five but within ten years	0
After ten years	0
Cost basis	1,043	1,014
Carrying value
Within one year	188
After one but within five years	833
After five but within ten years	0
After ten years	0
Total	$ 1,021	986
Weighted-average yield
Within one year (in hundredths)	2.28%
After one but within five years (in hundredths)	2.78%
After five but within ten years (in hundredths)	0.00%
After ten years (in hundredths)	0.00%
Total (in hundredths)	2.69%
Bank | Corporate bonds
Amortized cost
Within one year	$ 1
After one but within five years	116
After five but within ten years	28
After ten years	0
Cost basis	145	146
Carrying value
Within one year	1
After one but within five years	112
After five but within ten years	27
After ten years	0
Total	$ 140	141
Weighted-average yield
Within one year (in hundredths)	2.88%
After one but within five years (in hundredths)	5.80%
After five but within ten years (in hundredths)	4.95%
After ten years (in hundredths)	0.00%
Total (in hundredths)	5.61%
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	7
Cost basis	17	18
Carrying value
Within one year	0
After one but within five years	5
After five but within ten years	4
After ten years	8
Total	$ 17	$ 17
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	6.66%
After five but within ten years (in hundredths)	5.23%
After ten years (in hundredths)	7.47%
Total (in hundredths)	6.67%