Income Taxes - Differences between U.S. Federal Statutory Income Tax Rate of 35% and Income Taxes Provided (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Taxes on income at the U.S. federal statutory rate									$ 108	$ (1)	$ 14
U.S. state and local taxes									7	3	(1)
Foreign income taxed at different rates, including withholding taxes									19	11	12
Increase in valuation allowance									4	18	19
Release of valuation allowance									(14)	(134)	(26)
Change in tax rates									23	(1)	(10)
Intergroup transfer									(30)
Foreign currency losses on intra-entity loans										(59)
Non-deductible long term incentive plan									8	10	1
Other									5	2	2
Total	$ (2)	$ 61	$ 19	$ 52	$ (19)	$ (152)	$ 3	$ 17	$ 130	$ (151)	$ 11