Shareholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	$ (714)	$ (562)	$ (681)	$ (566)
Other comprehensive income before reclassification	10	(6)	(28)	(4)
Amounts reclassified from accumulated other comprehensive loss	3	(1)	8	1
Net current-period other comprehensive income	13	(7)	(20)	(3)
Ending balance	(701)	(569)	(701)	(569)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(142)	(87)	(107)	(90)
Other comprehensive income before reclassification	10	(6)	(25)	(3)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net current-period other comprehensive income	10	(6)	(25)	(3)
Ending balance	(132)	(93)	(132)	(93)
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(567)	(475)	(572)	(476)
Other comprehensive income before reclassification	0	0	0	(1)
Amounts reclassified from accumulated other comprehensive loss	3	1	8	3
Net current-period other comprehensive income	3	1	8	2
Ending balance	(564)	(474)	(564)	(474)
Unrealized Income (Loss) on cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(5)	0	(2)	0
Other comprehensive income before reclassification	0	0	(3)	0
Amounts reclassified from accumulated other comprehensive loss	0	(2)	0	(2)
Net current-period other comprehensive income	0	(2)	(3)	(2)
Ending balance	$ (5)	$ (2)	$ (5)	$ (2)