ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS), Schedule of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period			$ 6,643
OCI:
Total other comprehensive income/(loss), net of tax	$ 12	$ 11	24	$ 17
Balance end of period	7,015	6,564	7,015	6,564
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	149	114	110	88
OCI:
OCI before reclassifications and taxes	(29)	(16)	23	18
Amounts reclassified from AOCI, before tax	0	0	0	0
Pre-tax net OCI	(29)	(16)	23	18
Income tax effect	8	4	(5)	(4)
Total other comprehensive income/(loss), net of tax	(21)	(12)	18	14
Balance end of period	128	102	128	102
Net investment hedges | Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period				0
Currency translations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	(191)	(142)	(135)	(111)
OCI:
OCI before reclassifications and taxes	32	18	(24)	(13)
Amounts reclassified from AOCI, before tax	0	0	0	0
Pre-tax net OCI	32	18	(24)	(13)
Income tax effect	0	0	0	0
Total other comprehensive income/(loss), net of tax	32	18	(24)	(13)
Balance end of period	(159)	(124)	(159)	(124)
Currency translations | Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period				0
Subtotal: net investment hedges and currency translations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	(42)	(28)	(25)	(23)
OCI:
OCI before reclassifications and taxes	3	2	(1)	5
Amounts reclassified from AOCI, before tax	0	0	0	0
Pre-tax net OCI	3	2	(1)	5
Income tax effect	8	4	(5)	(4)
Total other comprehensive income/(loss), net of tax	11	6	(6)	1
Balance end of period	(31)	(22)	(31)	(22)
Subtotal: net investment hedges and currency translations | Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period				0
Available- for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	83	(9)	21	(46)
OCI:
OCI before reclassifications and taxes	7	32	90	90
Amounts reclassified from AOCI, before tax	0	0	0	0
Pre-tax net OCI	7	32	90	90
Income tax effect	(2)	(8)	(23)	(25)
Total other comprehensive income/(loss), net of tax	5	24	67	65
Balance end of period	88	15	88	15
Available- for-sale securities | Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period				(4)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	(52)	12	(19)	42
OCI:
OCI before reclassifications and taxes	(7)	(24)	(51)	(64)
Amounts reclassified from AOCI, before tax	2	(1)	2	(4)
Pre-tax net OCI	(5)	(25)	(49)	(68)
Income tax effect	1	6	12	19
Total other comprehensive income/(loss), net of tax	(4)	(19)	(37)	(49)
Balance end of period	(56)	(7)	(56)	(7)
Cash flow hedges | Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period				0
Accumulated other comprehensive income/ (loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	(11)	(25)	(23)	(27)
OCI:
OCI before reclassifications and taxes	3	10	38	31
Amounts reclassified from AOCI, before tax	2	(1)	2	(4)
Pre-tax net OCI	5	9	40	27
Income tax effect	7	2	(16)	(10)
Total other comprehensive income/(loss), net of tax	12	11	24	17
Balance end of period	$ 1	$ (14)	$ 1	(14)
Accumulated other comprehensive income/ (loss) | Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period				$ (4)