Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,625	$ 1,389
Other comprehensive income (loss) before reclassifications	(59)	66
Amounts reclassified from AOCI	(3)	2
Less: Other comprehensive income (loss) attributable to noncontrolling interests	(4)	2
Ending Balance	1,279	1,625
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(204)	(227)
Other comprehensive income (loss) before reclassifications	(64)	25
Amounts reclassified from AOCI	(2)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	(4)	2
Ending Balance	(266)	(204)
Unrealized Gains on Investment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	2	2
Other comprehensive income (loss) before reclassifications	(1)
Ending Balance	1	2
Pension and Other Postretirement Benefit Liability Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(57)	(100)
Other comprehensive income (loss) before reclassifications	6	41
Amounts reclassified from AOCI	(1)	2
Ending Balance	(52)	(57)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(259)	(325)
Amounts reclassified from AOCI	(3)	2
Ending Balance	$ (317)	$ (259)