Shareholders' Equity - Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	$ (2,283)	$ (1,909)	$ (1,723)
Other comprehensive (loss) income before reclassifications, net of taxes	(338)	(427)	(142)
Amounts reclassified into income, net of taxes	74	52	57
Accumulated other comprehensive (loss) income, ending balance	(2,548)	(2,283)	(1,909)
OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTaxAdjustmentDueToNewAccountingPrinciple			(103)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(1,256)	(1,162)	(1,001)
Other comprehensive (loss) income before reclassifications, net of taxes	(161)	(93)	(161)
Amounts reclassified into income, net of taxes	0	0	0
Accumulated other comprehensive (loss) income, ending balance	(1,416)	(1,256)	(1,162)
OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTaxAdjustmentDueToNewAccountingPrinciple			0
Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(1,005)	(729)	(703)
Other comprehensive (loss) income before reclassifications, net of taxes	(101)	(325)	19
Amounts reclassified into income, net of taxes	66	49	52
Accumulated other comprehensive (loss) income, ending balance	(1,040)	(1,005)	(729)
OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTaxAdjustmentDueToNewAccountingPrinciple			(99)
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(23)	(17)	(18)
Other comprehensive (loss) income before reclassifications, net of taxes	(76)	(9)	0
Amounts reclassified into income, net of taxes	8	3	5
Accumulated other comprehensive (loss) income, ending balance	$ (91)	$ (23)	(17)
OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTaxAdjustmentDueToNewAccountingPrinciple			$ (4)