FAIR VALUE, Recurring Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022
Assets at fair value on a recurring basis:
Available-for-sale securities	$ 9,793	$ 9,885
Derivative assets, gross	434	536
Amount of derivative assets offset	(327)	(348)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	107	188
Liabilities at fair value on a recurring basis:
Derivative liabilities	513	595
Total amounts offset	(61)	(65)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	452	530
Recurring
Assets at fair value on a recurring basis:
Total debt securities	1,059	1,219
Equity securities	18	20
Brokered certificates of deposit	29	30
Other	6	1
Total trading assets	1,112	1,270
Available-for-sale securities	9,793	9,885
Amount of derivative assets offset	(327)	(348)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	107	188
Other	202	202
Other assets - fractional shares	86	78
Assets at fair value on a recurring basis	11,394	11,713
Netting adjustments	(327)	(348)
Liabilities at fair value on a recurring basis:
Total debt securities	668	809
Equity securities	24	27
Total trading instruments sold but not yet purchased	692	836
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	452	530
Other payables - fractional shares	86	78
Netting adjustments	(61)	(65)
Total liabilities at fair value on a recurring basis	1,230	1,444
Recurring | Interest rate
Assets at fair value on a recurring basis:
Interest rate - matched book	14	52
Amount of derivative assets offset	(327)	(348)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	93	126
Liabilities at fair value on a recurring basis:
Interest rate - matched book	14	52
Total amounts offset	(61)	(65)
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	421	470
Recurring | Foreign exchange
Assets at fair value on a recurring basis:
Interest rate - matched book		10
Liabilities at fair value on a recurring basis:
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	13	5
Recurring | Other
Liabilities at fair value on a recurring basis:
Net amounts presented on the Condensed Consolidated Statements of Financial Condition	4	3
Recurring | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	6	5
Recurring | Corporate obligations
Liabilities at fair value on a recurring basis:
Total debt securities	525	555
Recurring | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	137	249
Recurring | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	163	269
Recurring | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	602	595
Recurring | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	126	171
Other	80	79
Recurring | Agency mortgage-backed securities (“MBS”), collateralized mortgage obligations (“CMOs”) and asset-backed securities (“ABS”)
Assets at fair value on a recurring basis:
Total debt securities	134	123
Recurring | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	34	61
Recurring | Other
Assets at fair value on a recurring basis:
Other	122	123
Recurring | Assets at Fair Value on a Recurring Basis, Before Investments Measured at NAV
Assets at fair value on a recurring basis:
Assets at fair value on a recurring basis	11,300	11,623
Recurring | Private equity investments
Assets at fair value on a recurring basis:
Private equity investments measured at NAV	94	90
Recurring | Level 1
Assets at fair value on a recurring basis:
Total debt securities	66	102
Equity securities	17	20
Brokered certificates of deposit	0	0
Other	0	0
Total trading assets	83	122
Available-for-sale securities	987	986
Derivative assets, gross	2	42
Other	170	171
Other assets - fractional shares	86	78
Assets at fair value on a recurring basis	1,328	1,399
Liabilities at fair value on a recurring basis:
Total debt securities	143	254
Equity securities	24	27
Total trading instruments sold but not yet purchased	167	281
Derivative contracts liability, gross	3	40
Other payables - fractional shares	86	78
Total liabilities at fair value on a recurring basis	256	399
Recurring | Level 1 | Interest rate
Assets at fair value on a recurring basis:
Interest rate - matched book	0	0
Derivative assets, gross	2	42
Liabilities at fair value on a recurring basis:
Interest rate - matched book	0	0
Derivative liabilities	3	40
Recurring | Level 1 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets, gross		0
Liabilities at fair value on a recurring basis:
Derivative contracts liability, gross	0	0
Recurring | Level 1 | Other
Liabilities at fair value on a recurring basis:
Derivative liabilities	0	0
Recurring | Level 1 | Municipal and provincial obligations
Liabilities at fair value on a recurring basis:
Total debt securities	6	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	137	249
Recurring | Level 1 | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 1 | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	19	16
Recurring | Level 1 | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	47	86
Other	80	79
Recurring | Level 1 | Agency mortgage-backed securities (“MBS”), collateralized mortgage obligations (“CMOs”) and asset-backed securities (“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 at fair value on a recurring basis:
Other	90	92
Recurring | Level 2
Assets at fair value on a recurring basis:
Total debt securities	993	1,117
Equity securities	1	0
Brokered certificates of deposit	29	30
Other	0	0
Total trading assets	1,023	1,147
Available-for-sale securities	8,806	8,899
Derivative assets, gross	432	494
Other	2	2
Other assets - fractional shares	0	0
Assets at fair value on a recurring basis	10,263	10,542
Liabilities at fair value on a recurring basis:
Total debt securities	525	555
Equity securities	0	0
Total trading instruments sold but not yet purchased	525	555
Derivative contracts liability, gross	506	552
Other payables - fractional shares	0	0
Total liabilities at fair value on a recurring basis	1,031	1,107
Recurring | Level 2 | Interest rate
Assets at fair value on a recurring basis:
Interest rate - matched book	14	52
Derivative assets, gross	418	432
Liabilities at fair value on a recurring basis:
Interest rate - matched book	14	52
Derivative liabilities	479	495
Recurring | Level 2 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets, gross		10
Liabilities at fair value on a recurring basis:
Derivative liabilities	13	5
Recurring | Level 2 | Other
Liabilities at fair value on a recurring basis:
Derivative liabilities	0	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	525	555
Recurring | Level 2 | Government and agency obligations
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Recurring | Level 2 | Municipal and provincial obligations
Assets at fair value on a recurring basis:
Total debt securities	163	269
Recurring | Level 2 | Corporate obligations
Assets at fair value on a recurring basis:
Total debt securities	583	579
Recurring | Level 2 | Government and agency obligations
Assets at fair value on a recurring basis:
Total debt securities	79	85
Other	0	0
Recurring | Level 2 | Agency mortgage-backed securities (“MBS”), collateralized mortgage obligations (“CMOs”) and asset-backed securities (“ABS”)
Assets at fair value on a recurring basis:
Total debt securities	134	123
Recurring | Level 2 | Non-agency CMOs and ABS
Assets at fair value on a recurring basis:
Total debt securities	34	61
Recurring | Level 2 | Other
Assets at fair value on a recurring basis:
Other	2	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	6	1
Total trading assets	6	1
Available-for-sale securities	0	0
Derivative assets, gross	0	0
Other	30	29
Other assets - fractional shares	0	0
Assets at fair value on a recurring basis	36	30
Liabilities at fair value on a recurring basis:
Total debt securities	0	0
Equity securities	0	0
Total trading instruments sold but not yet purchased	0	0
Derivative contracts liability, gross	4	3
Other payables - fractional shares	0	0
Total liabilities at fair value on a recurring basis	4	3
Recurring | Level 3 | Interest rate
Assets at fair value on a recurring basis:
Interest rate - matched book	0	0
Derivative assets, gross	0	0
Liabilities at fair value on a recurring basis:
Interest rate - matched book	0	0
Derivative liabilities	0	0
Recurring | Level 3 | Foreign exchange
Assets at fair value on a recurring basis:
Derivative assets, gross		0
Liabilities at fair value on a recurring basis:
Derivative contracts liability, gross	0	0
Recurring | Level 3 | Other
Liabilities at fair value on a recurring basis:
Derivative liabilities	4	3
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 | 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
Other	0	0
Recurring | Level 3 | Agency mortgage-backed securities (“MBS”), collateralized mortgage obligations (“CMOs”) and asset-backed securities (“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 at fair value on a recurring basis:
Other	$ 30	$ 29