Stockholders' Deficit - Schedule of Reclassifications From Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension and other postretirement benefit plan remeasurement (gain) loss	$ (126)	$ (59)	$ 60
(Gain) loss on liquidation of subsidiary	(44)	(34)	(40)
Income tax expense (benefit)	123	134	57
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension and other postretirement benefit plan remeasurement (gain) loss	(12)	(12)	(12)
(Gain) loss on liquidation of subsidiary	0	1	(1)
Gain (Loss) on Hedging Activity	1	0	0
Income tax expense (benefit)	3	3	3
Other Comprehensive Income (Loss), Net of Tax	$ (10)	$ (8)	$ (10)