FAIR VALUE, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Assets at fair value on a recurring basis:
Available-for-sale securities	$ 6,888	$ 8,260
Derivative assets	307	349
Netting adjustments	(239)	(246)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	68	103
Liabilities at fair value on a recurring basis:
Derivative liability	313	347
Netting adjustment	(123)	(123)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	190	224
Recurring
Assets at fair value on a recurring basis:
Total debt securities	1,495	1,441
Equity securities	20	16
Brokered certificates of deposit	19	20
Other	4	3
Total trading assets	1,538	1,480
Available-for-sale securities	6,888	8,260
Netting adjustments	(239)	(246)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	68	103
Total all other investments	285	200
Other assets - client-owned fractional shares	171	133
Total assets at fair value on a recurring basis	9,055	10,278
Other investments - private equity - measured at NAV	105	102
Liabilities at fair value on a recurring basis:
Total debt securities	860	878
Equity securities	31	98
Total trading liabilities	891	976
Netting adjustment	(123)	(123)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	190	224
Other payables - repurchase liabilities related to client-owned fractional shares	171	133
Total liabilities at fair value on a recurring basis	1,252	1,333
Recurring | Interest rate
Assets at fair value on a recurring basis:
Netting adjustments	(239)	(246)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	67	92
Liabilities at fair value on a recurring basis:
Netting adjustment	(123)	(123)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	186	223
Recurring | Foreign exchange
Assets at fair value on a recurring basis:
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	1	7
Liabilities at fair value on a recurring basis:
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	2	1
Recurring | Other
Assets at fair value on a recurring basis:
Net amounts presented on the Condensed Consolidated Statements of Financial Condition		4
Liabilities at fair value on a recurring basis:
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	2
Recurring | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	3	5
Recurring | Corporate obligations
Liabilities at fair value on a recurring basis:
Total debt securities	651	598
Recurring | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	164	249
Recurring | Agency MBS and CMOs
Liabilities at fair value on a recurring basis:
Total debt securities	42	26
Recurring | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	409	306
Recurring | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	670	642
Recurring | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	149	193
Total all other investments	92	91
Recurring | Agency MBS, CMOs, and ABS
Assets at fair value on a recurring basis:
Total debt securities	231	205
Recurring | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	36	95
Recurring | Other assets
Assets at fair value on a recurring basis:
Total all other investments	193	109
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	8,950	10,176
Recurring | Level 1
Assets at fair value on a recurring basis:
Total debt securities	58	63
Equity securities	17	14
Brokered certificates of deposit	0	0
Other	0	0
Total trading assets	75	77
Available-for-sale securities	430	704
Derivative assets	2	3
Total all other investments	277	192
Other assets - client-owned fractional shares	171	133
Total assets at fair value on a recurring basis	955	1,109
Liabilities at fair value on a recurring basis:
Total debt securities	167	248
Equity securities	31	97
Total trading liabilities	198	345
Derivative liability	3	3
Other payables - repurchase liabilities related to client-owned fractional shares	171	133
Total liabilities at fair value on a recurring basis	372	481
Recurring | Level 1 | Interest rate
Assets at fair value on a recurring basis:
Derivative assets	2	3
Liabilities at fair value on a recurring basis:
Derivative liability	3	3
Recurring | Level 1 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets	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		0
Liabilities at fair value on a recurring basis:
Derivative liability	0
Recurring | Level 1 | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	3	5
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	164	243
Recurring | Level 1 | Agency MBS and CMOs
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 1 | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	6	2
Recurring | Level 1 | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	11	12
Recurring | Level 1 | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	41	49
Total all other investments	92	91
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	185	101
Recurring | Level 2
Assets at fair value on a recurring basis:
Total debt securities	1,437	1,378
Equity securities	3	2
Brokered certificates of deposit	19	20
Other	0	0
Total trading assets	1,459	1,400
Available-for-sale securities	6,458	7,556
Derivative assets	305	342
Total all other investments	1	1
Other assets - client-owned fractional shares	0	0
Total assets at fair value on a recurring basis	8,223	9,299
Liabilities at fair value on a recurring basis:
Total debt securities	693	630
Equity securities	0	1
Total trading liabilities	693	631
Derivative liability	308	344
Other payables - repurchase liabilities related to client-owned fractional shares	0	0
Total liabilities at fair value on a recurring basis	1,001	975
Recurring | Level 2 | Interest rate
Assets at fair value on a recurring basis:
Derivative assets	304	335
Liabilities at fair value on a recurring basis:
Derivative liability	306	343
Recurring | Level 2 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets	1	7
Liabilities at fair value on a recurring basis:
Derivative liability	2	1
Recurring | Level 2 | Other
Assets at fair value on a recurring basis:
Derivative assets		0
Liabilities at fair value on a recurring basis:
Derivative liability	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	651	598
Recurring | Level 2 | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	0	6
Recurring | Level 2 | Agency MBS and CMOs
Liabilities at fair value on a recurring basis:
Total debt securities	42	26
Recurring | Level 2 | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	403	304
Recurring | Level 2 | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	659	630
Recurring | Level 2 | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	108	144
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	231	205
Recurring | Level 2 | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	36	95
Recurring | Level 2 | Other assets
Assets at fair value on a recurring basis:
Total all other investments	1	1
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	4	3
Total trading assets	4	3
Available-for-sale securities	0	0
Derivative assets	0	4
Total all other investments	7	7
Other assets - client-owned fractional shares	0	0
Total assets at fair value on a recurring basis	11	14
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Equity securities	0	0
Total trading liabilities	0	0
Derivative liability	2	0
Other payables - repurchase liabilities related to client-owned fractional shares	0	0
Total liabilities at fair value on a recurring basis	2	0
Recurring | Level 3 | Interest rate
Assets at fair value on a recurring basis:
Derivative assets	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	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		4
Liabilities at fair value on a recurring basis:
Derivative liability	2
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	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	$ 7