AVAILABLE-FOR-SALE SECURITIES, Contractual Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022
Carrying value
Total	$ 9,793	$ 9,885
Bank
Amortized cost
Within one year	110
After one but within five years	2,554
After five but within ten years	3,210
After ten years	5,048
Cost basis	10,922	11,100
Carrying value
Within one year	107
After one but within five years	2,419
After five but within ten years	2,851
After ten years	4,416
Total	$ 9,793	9,885
Weighted-average yield
Within one year (in hundredths)	2.22%
After one but within five years (in hundredths)	2.48%
After five but within ten years (in hundredths)	1.39%
After ten years (in hundredths)	2.01%
Total (in hundredths)	1.94%
Bank | Agency residential MBS
Amortized cost
Within one year	$ 0
After one but within five years	142
After five but within ten years	2,427
After ten years	2,917
Cost basis	5,486	5,662
Carrying value
Within one year	0
After one but within five years	137
After five but within ten years	2,189
After ten years	2,573
Total	$ 4,899	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)	1.28%
After ten years (in hundredths)	1.88%
Total (in hundredths)	1.63%
Bank | Agency commercial MBS
Amortized cost
Within one year	$ 2
After one but within five years	803
After five but within ten years	607
After ten years	72
Cost basis	1,484	1,518
Carrying value
Within one year	2
After one but within five years	725
After five but within ten years	497
After ten years	61
Total	$ 1,285	1,310
Weighted-average yield
Within one year (in hundredths)	1.90%
After one but within five years (in hundredths)	1.67%
After five but within ten years (in hundredths)	1.23%
After ten years (in hundredths)	1.55%
Total (in hundredths)	1.48%
Bank | Agency CMOs
Amortized cost
Within one year	$ 0
After one but within five years	11
After five but within ten years	29
After ten years	1,545
Cost basis	1,585	1,637
Carrying value
Within one year	0
After one but within five years	11
After five but within ten years	25
After ten years	1,309
Total	$ 1,345	1,404
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	2.22%
After five but within ten years (in hundredths)	1.56%
After ten years (in hundredths)	1.57%
Total (in hundredths)	1.57%
Bank | Other agency obligations
Amortized cost
Within one year	$ 0
After one but within five years	567
After five but within ten years	114
After ten years	11
Cost basis	692	613
Carrying value
Within one year	0
After one but within five years	544
After five but within ten years	108
After ten years	11
Total	$ 663	582
Weighted-average yield
Within one year (in hundredths)	0.00%
After one but within five years (in hundredths)	2.64%
After five but within ten years (in hundredths)	3.55%
After ten years (in hundredths)	2.94%
Total (in hundredths)	2.80%
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	495
Cost basis	495	492
Carrying value
Within one year	0
After one but within five years	0
After five but within ten years	0
After ten years	454
Total	$ 454	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)	4.06%
Total (in hundredths)	4.06%
Bank | U.S. Treasuries
Amortized cost
Within one year	$ 107
After one but within five years	909
After five but within ten years	0
After ten years	0
Cost basis	1,016	1,014
Carrying value
Within one year	104
After one but within five years	883
After five but within ten years	0
After ten years	0
Total	$ 987	986
Weighted-average yield
Within one year (in hundredths)	2.22%
After one but within five years (in hundredths)	2.69%
After five but within ten years (in hundredths)	0.00%
After ten years (in hundredths)	0.00%
Total (in hundredths)	2.63%
Bank | Corporate bonds
Amortized cost
Within one year	$ 1
After one but within five years	117
After five but within ten years	28
After ten years	0
Cost basis	146	146
Carrying value
Within one year	1
After one but within five years	114
After five but within ten years	27
After ten years	0
Total	$ 142	141
Weighted-average yield
Within one year (in hundredths)	2.83%
After one but within five years (in hundredths)	5.51%
After five but within ten years (in hundredths)	4.86%
After ten years (in hundredths)	0.00%
Total (in hundredths)	5.37%
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)	5.79%
After five but within ten years (in hundredths)	5.23%
After ten years (in hundredths)	7.17%
Total (in hundredths)	6.30%