Shareholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	$ (681)	$ (566)
Other comprehensive income before reclassification	21	(5)
Amounts reclassified from accumulated other comprehensive loss	5	2
Net current-period other comprehensive income	26	(3)
Ending balance	(655)	(569)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(107)	(90)
Other comprehensive income before reclassification	21	(4)
Amounts reclassified from accumulated other comprehensive loss	0	0
Net current-period other comprehensive income	21	(4)
Ending balance	(86)	(94)
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(572)	(476)
Other comprehensive income before reclassification	0	(1)
Amounts reclassified from accumulated other comprehensive loss	3	1
Net current-period other comprehensive income	3	0
Ending balance	(569)	(476)
Unrealized Income (Loss) on cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(2)	0
Other comprehensive income before reclassification	0	0
Amounts reclassified from accumulated other comprehensive loss	2	1
Net current-period other comprehensive income	2	1
Ending balance	$ 0	$ 1