Shareholders' Equity - Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	$ (1,929)	$ (1,738)	$ (1,001)
Other comprehensive loss before reclassifications, net of taxes	140	(251)	(787)
Amounts reclassified into income, net of taxes	66	60	50
Accumulated other comprehensive (loss) income, ending balance	(1,723)	(1,929)	(1,738)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(1,011)	(961)	(270)
Other comprehensive loss before reclassifications, net of taxes	11	(50)	(692)
Amounts reclassified into income, net of taxes	0	0	0
Accumulated other comprehensive (loss) income, ending balance	(1,001)	(1,011)	(961)
Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(883)	(741)	(705)
Other comprehensive loss before reclassifications, net of taxes	121	(190)	(80)
Amounts reclassified into income, net of taxes	58	48	44
Accumulated other comprehensive (loss) income, ending balance	(703)	(883)	(741)
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated other comprehensive (loss) income, beginning balance	(35)	(36)	(26)
Other comprehensive loss before reclassifications, net of taxes	8	(11)	(16)
Amounts reclassified into income, net of taxes	8	12	6
Accumulated other comprehensive (loss) income, ending balance	$ (18)	$ (35)	$ (36)