Income Taxes - Consolidated Income (Loss) Before Income Taxes and Noncontrolling Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	$ 2	$ (1,121)	$ 1,061
Foreign tax authority | Ireland
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	(1)	4	(6)
Foreign tax authority | Other Foreign
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	173	(801)	945
United States
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	$ (170)	$ (324)	$ 122