Shareholders' Equity - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Employee Benefit Related Adjustment	$ 14	$ 23	$ 28	$ 37
Tax benefit	(15)	(22)	(27)	(29)
NET INCOME	65	66	123	99
Amount Reclassified from Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
NET INCOME	0	2	2	4
Amount Reclassified from Accumulated Other Comprehensive Income | Prior service benefit
Accumulated Other Comprehensive Income (Loss) [Line Items]
Employee Benefit Related Adjustment	(9)	(9)	(17)	(18)
Amount Reclassified from Accumulated Other Comprehensive Income | Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Employee Benefit Related Adjustment	9	11	19	22
Amount Reclassified from Accumulated Other Comprehensive Income | Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	0	2	2	4
Tax benefit	$ 0	$ 0	$ 0	$ 0