Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,372	$ 1,338	$ 2,064
Other comprehensive income (loss)	68	(31)	(239)
Other comprehensive income (loss) before reclassifications	66
Amounts reclassified from AOCI	2
Less: Other comprehensive income (loss) attributable to noncontrolling interests	2	(5)
Ending Balance	1,601	1,372	1,338
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(227)	(239)
Other comprehensive income (loss)		7
Other comprehensive income (loss) before reclassifications	25
Less: Other comprehensive income (loss) attributable to noncontrolling interests	2	(5)
Ending Balance	(204)	(227)	(239)
Unrealized Gains on Investment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	2	2
Ending Balance	2	2	2
Pension and Other Postretirement Benefit Liability Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(100)	(62)
Other comprehensive income (loss)		(38)
Other comprehensive income (loss) before reclassifications	41
Amounts reclassified from AOCI	2		24
Ending Balance	(57)	(100)	(62)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(325)	(299)	(64)
Other comprehensive income (loss)	66	(26)	(235)
Ending Balance	$ (259)	$ (325)	$ (299)