Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,276	$ 1,279	$ 1,472	$ 1,279	$ 1,625
Ending Balance	1,232	1,276	1,343	1,232	1,343
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(291)	(266)		(266)
Other comprehensive income (loss) before reclassifications	8	(24)
Amounts reclassified from AOCI	(1)	(1)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	2
Ending Balance	(286)	(291)		(286)
Unrealized Gains on Investments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	1	1		1
Ending Balance	1	1		1
Pension and Other Postretirement Benefit Liability Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(30)	(52)		(52)
Other comprehensive income (loss) before reclassifications	1	30
Amounts reclassified from AOCI	(1)	(8)
Ending Balance	(30)	(30)		(30)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(320)	(317)	(263)	(317)	(259)
Other comprehensive income (loss) before reclassifications	9	6
Amounts reclassified from AOCI	(2)	(9)	(1)	(11)	(2)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	2
Ending Balance	$ (315)	$ (320)	$ (209)	$ (315)	$ (209)