Shareholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	$ 565	$ 384	$ 495	$ 415
Other comprehensive income before reclassification	(22)	(59)	35	(38)
Amounts reclassified from accumulated other comprehensive loss	2	0	4	5
Net current-period other comprehensive income	(20)	(59)	39	(33)
Ending Balance	613	424	613	424
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(74)	(86)	(129)	(107)
Other comprehensive income before reclassification	(22)	(56)	33	(35)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net current-period other comprehensive income	(22)	(56)	33	(35)
Ending Balance	(96)	(142)	(96)	(142)
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(480)	(569)	(483)	(572)
Other comprehensive income before reclassification	0	0	1	0
Amounts reclassified from accumulated other comprehensive loss	2	2	4	5
Net current-period other comprehensive income	2	2	5	5
Ending Balance	(478)	(567)	(478)	(567)
Unrealized Income (Loss) on cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(1)	0	(2)	(2)
Other comprehensive income before reclassification	0	(3)	1	(3)
Amounts reclassified from accumulated other comprehensive loss	0	(2)	0	0
Net current-period other comprehensive income	0	(5)	1	(3)
Ending Balance	(1)	(5)	(1)	(5)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(555)	(655)	(614)	(681)
Ending Balance	$ (575)	$ (714)	$ (575)	$ (714)