Shareholders' Equity - Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	$ (1,723)	$ (1,929)	$ (1,738)
Other comprehensive loss before reclassifications, net of taxes	(142)	140	(251)
Amounts reclassified into income, net of taxes	57	66	60
Tax effects reclassified to retained earnings	(103)
Accumulated other comprehensive (loss) income, ending balance	(1,909)	(1,723)	(1,929)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(1,001)	(1,011)	(961)
Other comprehensive loss before reclassifications, net of taxes	(161)	11	(50)
Amounts reclassified into income, net of taxes	0	0	0
Tax effects reclassified to retained earnings	0
Accumulated other comprehensive (loss) income, ending balance	(1,162)	(1,001)	(1,011)
Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(703)	(883)	(741)
Other comprehensive loss before reclassifications, net of taxes	19	121	(190)
Amounts reclassified into income, net of taxes	52	58	48
Tax effects reclassified to retained earnings	(99)
Accumulated other comprehensive (loss) income, ending balance	(729)	(703)	(883)
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(18)	(35)	(36)
Other comprehensive loss before reclassifications, net of taxes	0	8	(11)
Amounts reclassified into income, net of taxes	5	8	12
Tax effects reclassified to retained earnings	(4)
Accumulated other comprehensive (loss) income, ending balance	$ (17)	$ (18)	$ (35)