Leases - Narrative (Details) - USD ($) $ in Millions	Oct. 01, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-02 [Member]
Operating lease right-of-use assets		$ 335	$ 334
Present value of lease liabilities		335	339
Stockholders' equity, including portion attributable to noncontrolling interest		$ 2,718	1,535	$ 2,189	$ 2,717
Cumulative effect, period of adoption, adjustment
Operating lease right-of-use assets	$ 380		380
Present value of lease liabilities	384		$ 384
Stockholders' equity, including portion attributable to noncontrolling interest	$ (4)			$ (4)