ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS), Schedule of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	$ 7,176
OCI:
OCI before reclassifications and taxes	(8)	$ 17
Amounts reclassified from AOCI, before tax	1	0
Pre-tax net OCI	(7)	17
Income tax effect	13	1
Total other comprehensive income, net of tax	6	18
Balance end of period	7,438	6,903
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	115	110
OCI:
OCI before reclassifications and taxes	(38)	(17)
Amounts reclassified from AOCI, before tax	0	0
Pre-tax net OCI	(38)	(17)
Income tax effect	9	4
Total other comprehensive income, net of tax	(29)	(13)
Balance end of period	86	97
Currency translations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	(140)	(135)
OCI:
OCI before reclassifications and taxes	45	22
Amounts reclassified from AOCI, before tax	2	0
Pre-tax net OCI	47	22
Income tax effect	0	0
Total other comprehensive income, net of tax	47	22
Balance end of period	(93)	(113)
Subtotal: net investment hedges and currency translations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	(25)	(25)
OCI:
OCI before reclassifications and taxes	7	5
Amounts reclassified from AOCI, before tax	2	0
Pre-tax net OCI	9	5
Income tax effect	9	4
Total other comprehensive income, net of tax	18	9
Balance end of period	(7)	(16)
Available- for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	89	21
OCI:
OCI before reclassifications and taxes	(18)	(2)
Amounts reclassified from AOCI, before tax	(5)	0
Pre-tax net OCI	(23)	(2)
Income tax effect	6	1
Total other comprehensive income, net of tax	(17)	(1)
Balance end of period	72	20
Cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	(53)	(19)
OCI:
OCI before reclassifications and taxes	3	14
Amounts reclassified from AOCI, before tax	4	0
Pre-tax net OCI	7	14
Income tax effect	(2)	(4)
Total other comprehensive income, net of tax	5	10
Balance end of period	(48)	(9)
Accumulated other comprehensive income/ (loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance beginning of period	11	(23)
OCI:
Total other comprehensive income, net of tax	6	18
Balance end of period	$ 17	$ (5)