ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS), AOCI Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	$ 6,643	$ 6,452
OCI for the year, net of tax	34	8	$ (12)
Balance, end of year	$ 7,176	$ 6,643	6,452
Accounting standards update	us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201601Member
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	$ 110	$ 88
OCI before reclassifications and taxes	7	29
Amounts reclassified from AOCI, before tax	0	0
Pre-tax net OCI	7	29
Income tax effect	(2)	(7)
OCI for the year, net of tax	5	22
Balance, end of year	115	110	88
Net investment hedges | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year		0
Balance, end of year			0
Currency translations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	(135)	(111)
OCI before reclassifications and taxes	(5)	(24)
Amounts reclassified from AOCI, before tax	0	0
Pre-tax net OCI	(5)	(24)
Income tax effect	0	0
OCI for the year, net of tax	(5)	(24)
Balance, end of year	(140)	(135)	(111)
Currency translations | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year		0
Balance, end of year			0
Subtotal: net investment hedges and currency translations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	(25)	(23)
OCI before reclassifications and taxes	2	5
Amounts reclassified from AOCI, before tax	0	0
Pre-tax net OCI	2	5
Income tax effect	(2)	(7)
OCI for the year, net of tax	0	(2)
Balance, end of year	(25)	(25)	(23)
Subtotal: net investment hedges and currency translations | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year		0
Balance, end of year			0
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	21	(46)
OCI before reclassifications and taxes	94	98
Amounts reclassified from AOCI, before tax	(3)	0
Pre-tax net OCI	91	98
Income tax effect	(23)	(27)
OCI for the year, net of tax	68	71
Balance, end of year	89	21	(46)
Available-for-sale securities | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year		(4)
Balance, end of year			(4)
Cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	(19)	42
OCI before reclassifications and taxes	(51)	(79)
Amounts reclassified from AOCI, before tax	5	(5)
Pre-tax net OCI	(46)	(84)
Income tax effect	12	23
OCI for the year, net of tax	(34)	(61)
Balance, end of year	(53)	(19)	42
Cash flow hedges | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year		0
Balance, end of year			0
Accumulated other comprehensive (loss) income
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year	(23)	(27)	(15)
OCI before reclassifications and taxes	45	24
Amounts reclassified from AOCI, before tax	2	(5)
Pre-tax net OCI	47	19
Income tax effect	(13)	(11)
OCI for the year, net of tax	34	8	(12)
Balance, end of year	$ 11	(23)	(27)
Accumulated other comprehensive (loss) income | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning of year		$ (4)
Balance, end of year			$ (4)