FAIR VALUE, Recurring and Nonrecurring Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Assets at fair value on a recurring basis:
Available-for-sale securities	$ 8,260	$ 9,181
Derivative assets, gross	349	526
Amount of derivative assets offset	(246)	(261)
Net amounts presented on the Consolidated Statements of Financial Condition	103	265
Liabilities at fair value on a recurring basis:
Derivative liability	347	578
Derivative liability, collateral, amount of offset	(123)	(88)
Net amounts presented on the Consolidated Statements of Financial Condition	224	490
Recurring
Assets at fair value on a recurring basis:
Total debt securities	1,441	1,125
Equity securities	16	22
Brokered certificates of deposit	20	36
Other	3	4
Total trading assets	1,480	1,187
Available-for-sale securities	8,260	9,181
Amount of derivative assets offset	(246)	(261)
Net amounts presented on the Consolidated Statements of Financial Condition	103	265
Total all other investments	200	205
Other assets - client-owned fractional shares	133	98
Total assets at fair value on a recurring basis	10,278	11,037
Netting adjustments	(246)	(261)
Other investments - private equity - measured at NAV	102	101
Liabilities at fair value on a recurring basis:
Total debt securities	878	686
Equity securities	98	30
Total trading liabilities	976	716
Net amounts presented on the Consolidated Statements of Financial Condition	224	490
Netting adjustment	(123)	(88)
Other payables - repurchase liabilities related to client-owned fractional shares	133	98
Total liabilities at fair value on a recurring basis	1,333	1,304
Recurring | Interest rate
Assets at fair value on a recurring basis:
Amount of derivative assets offset	(246)	(261)
Net amounts presented on the Consolidated Statements of Financial Condition	92	256
Liabilities at fair value on a recurring basis:
Derivative liability, collateral, amount of offset	(123)	(88)
Net amounts presented on the Consolidated Statements of Financial Condition	223	488
Recurring | Foreign exchange
Assets at fair value on a recurring basis:
Net amounts presented on the Consolidated Statements of Financial Condition	7	9
Liabilities at fair value on a recurring basis:
Net amounts presented on the Consolidated Statements of Financial Condition	1	2
Recurring | Other
Assets at fair value on a recurring basis:
Net amounts presented on the Consolidated Statements of Financial Condition	4
Recurring | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	5	10
Recurring | Corporate obligations
Liabilities at fair value on a recurring basis:
Total debt securities	598	514
Recurring | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	249	162
Recurring | Agency MBS and CMOs
Liabilities at fair value on a recurring basis:
Total debt securities	26
Recurring | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	306	239
Recurring | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	642	642
Recurring | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	193	141
Total all other investments	91	71
Recurring | Agency MBS, CMOs, and ABS
Assets at fair value on a recurring basis:
Total debt securities	205	35
Recurring | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	95	68
Recurring | Other assets
Assets at fair value on a recurring basis:
Total all other investments	109	134
Recurring | Assets at Fair Value on a Recurring Basis, Before Investments Measured at NAV
Assets at fair value on a recurring basis:
Total assets at fair value on a recurring basis	10,176	10,936
Recurring | Level 1
Assets at fair value on a recurring basis:
Total debt securities	63	46
Equity securities	14	20
Brokered certificates of deposit	0	0
Other	0	0
Total trading assets	77	66
Available-for-sale securities	704	1,240
Derivative assets, gross	3	14
Total all other investments	192	173
Other assets - client-owned fractional shares	133	98
Total assets at fair value on a recurring basis	1,109	1,591
Liabilities at fair value on a recurring basis:
Total debt securities	248	171
Equity securities	97	30
Total trading liabilities	345	201
Derivative contracts liability, gross	3	13
Other payables - repurchase liabilities related to client-owned fractional shares	133	98
Total liabilities at fair value on a recurring basis	481	312
Recurring | Level 1 | Interest rate
Assets at fair value on a recurring basis:
Derivative assets, gross	3	14
Liabilities at fair value on a recurring basis:
Derivative liability	3	13
Recurring | Level 1 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets, gross	0	0
Liabilities at fair value on a recurring basis:
Derivative liability	0	0
Recurring | Level 1 | Other
Assets at fair value on a recurring basis:
Derivative assets, gross	0
Recurring | Level 1 | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	5	10
Recurring | Level 1 | Corporate obligations
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 1 | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	243	161
Recurring | Level 1 | Agency MBS and CMOs
Liabilities at fair value on a recurring basis:
Total debt securities	0
Recurring | Level 1 | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	2	0
Recurring | Level 1 | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	12	22
Recurring | Level 1 | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	49	24
Total all other investments	91	71
Recurring | Level 1 | Agency MBS, CMOs, and ABS
Assets at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 1 | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 1 | Other assets
Assets at fair value on a recurring basis:
Total all other investments	101	102
Recurring | Level 2
Assets at fair value on a recurring basis:
Total debt securities	1,378	1,079
Equity securities	2	2
Brokered certificates of deposit	20	36
Other	0	0
Total trading assets	1,400	1,117
Available-for-sale securities	7,556	7,941
Derivative assets, gross	342	512
Total all other investments	1	2
Other assets - client-owned fractional shares	0	0
Total assets at fair value on a recurring basis	9,299	9,572
Liabilities at fair value on a recurring basis:
Total debt securities	630	515
Equity securities	1	0
Total trading liabilities	631	515
Derivative contracts liability, gross	344	565
Other payables - repurchase liabilities related to client-owned fractional shares	0	0
Total liabilities at fair value on a recurring basis	975	1,080
Recurring | Level 2 | Interest rate
Assets at fair value on a recurring basis:
Derivative assets, gross	335	503
Liabilities at fair value on a recurring basis:
Derivative liability	343	563
Recurring | Level 2 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets, gross	7	9
Liabilities at fair value on a recurring basis:
Derivative liability	1	2
Recurring | Level 2 | Other
Assets at fair value on a recurring basis:
Derivative assets, gross	0
Recurring | Level 2 | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 2 | Corporate obligations
Liabilities at fair value on a recurring basis:
Total debt securities	598	514
Recurring | Level 2 | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	6	1
Recurring | Level 2 | Agency MBS and CMOs
Liabilities at fair value on a recurring basis:
Total debt securities	26
Recurring | Level 2 | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	304	239
Recurring | Level 2 | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	630	620
Recurring | Level 2 | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	144	117
Total all other investments	0	0
Recurring | Level 2 | Agency MBS, CMOs, and ABS
Assets at fair value on a recurring basis:
Total debt securities	205	35
Recurring | Level 2 | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	95	68
Recurring | Level 2 | Other assets
Assets at fair value on a recurring basis:
Total all other investments	1	2
Recurring | Level 3
Assets at fair value on a recurring basis:
Total debt securities	0	0
Equity securities	0	0
Brokered certificates of deposit	0	0
Other	3	4
Total trading assets	3	4
Available-for-sale securities	0	0
Derivative assets, gross	4	0
Total all other investments	7	30
Other assets - client-owned fractional shares	0	0
Total assets at fair value on a recurring basis	14	34
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Equity securities	0	0
Total trading liabilities	0	0
Derivative contracts liability, gross	0	0
Other payables - repurchase liabilities related to client-owned fractional shares	0	0
Total liabilities at fair value on a recurring basis	0	0
Recurring | Level 3 | Interest rate
Assets at fair value on a recurring basis:
Derivative assets, gross	0	0
Liabilities at fair value on a recurring basis:
Derivative liability	0	0
Recurring | Level 3 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets, gross	0	0
Liabilities at fair value on a recurring basis:
Derivative liability	0	0
Recurring | Level 3 | Other
Assets at fair value on a recurring basis:
Derivative assets, gross	4
Recurring | Level 3 | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 3 | Corporate obligations
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 3 | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 3 | Agency MBS and CMOs
Liabilities at fair value on a recurring basis:
Total debt securities	0
Recurring | Level 3 | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 3 | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 3 | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	0	0
Total all other investments	0	0
Recurring | Level 3 | Agency MBS, CMOs, and ABS
Assets at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 3 | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 3 | Other assets
Assets at fair value on a recurring basis:
Total all other investments	$ 7	$ 30