Other Operating Income, Net and Other Non-Operating (Expense) Income, Net - Other Operating Income, Net (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Component of Operating Income [Abstract]
Finance charges	$ 9	$ 17	$ 16
Interest and interest-related income	2	6	3
Utility non-tariff service income	0	1	3
Gains on sales of fixed assets, net	5	3	5
Other, net	5	4	5
Total other operating income, net	$ 21	$ 31	$ 32

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Name:	us-gaap_GainLossOnSaleOfPropertyPlantEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration