Shareholders' Equity - Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	$ (1,909)	$ (1,723)	$ (1,929)
Other comprehensive income before reclassifications, net of taxes	(427)	(142)	140
Amounts reclassified into income, net of taxes	52	57	66
Tax effects reclassified to retained earnings		(103)
Accumulated other comprehensive (loss) income, ending balance	(2,283)	(1,909)	(1,723)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(1,162)	(1,001)	(1,011)
Other comprehensive income before reclassifications, net of taxes	(93)	(161)	11
Amounts reclassified into income, net of taxes	0	0	0
Tax effects reclassified to retained earnings		0
Accumulated other comprehensive (loss) income, ending balance	(1,256)	(1,162)	(1,001)
Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(729)	(703)	(883)
Other comprehensive income before reclassifications, net of taxes	(325)	19	121
Amounts reclassified into income, net of taxes	49	52	58
Tax effects reclassified to retained earnings		(99)
Accumulated other comprehensive (loss) income, ending balance	(1,005)	(729)	(703)
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(17)	(18)	(35)
Other comprehensive income before reclassifications, net of taxes	(9)	0	8
Amounts reclassified into income, net of taxes	3	5	8
Tax effects reclassified to retained earnings		(4)
Accumulated other comprehensive (loss) income, ending balance	$ (23)	$ (17)	$ (18)