Income Taxes - Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Accrued expenses and reserves	$ 73	$ 64
Employee and retiree benefits	43	35
Net operating loss and other credit carryforwards	751	527
Property, plant and equipment	161	163
Intangible assets	308	361
Research and development	16	16
Other	7	27
Deferred tax assets:	1,359	1,193
Valuation allowances	(1,304)	(846)
Deferred tax assets, net	55	347
Unremitted earnings of foreign subsidiaries	62	58
Deferred tax liabilities:	62	58
Net deferred tax liabilities	$ (7)
Net deferred tax asset		$ 289