Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,279	$ 1,625
Ending Balance	1,276	1,472
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(266)
Other comprehensive income (loss) before reclassifications	(24)
Amounts reclassified from AOCI	(1)
Ending Balance	(291)
Unrealized Gains on Investments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	1
Ending Balance	1
Pension and Other Postretirement Benefit Liability Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(52)
Other comprehensive income (loss) before reclassifications	30
Amounts reclassified from AOCI	(8)
Ending Balance	(30)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(317)	(259)
Other comprehensive income (loss) before reclassifications	6
Amounts reclassified from AOCI	(9)	(1)
Ending Balance	$ (320)	$ (263)