Supplementary Financial Information - Consolidated Statements of Operations Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
OTHER INCOME (EXPENSE), NET
Interest income	$ 2	$ 4	$ 5	$ 7
Foreign currency loss, net	(7)	(6)	(11)	(7)
Marketable Securities, Gain (Loss)	8	0	20	0
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	6	2	11	4
Change in fair value of emergence date warrants	6	3	3	21
Sublease Income	1	0	3	0
Other, net	(1)	(2)	(2)	(2)
Total other income (expense), net	15	1	29	23
Other income (expense), net	15	1	29	23
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	(6)	(2)	(11)	(4)
Change in fair value of emergence date warrants	$ (6)	$ (3)	$ (3)	$ (21)