Shareholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	$ (655)	$ (569)	$ (681)	$ (566)
Other comprehensive income before reclassification	(59)	7	(38)	2
Amounts reclassified from accumulated other comprehensive loss	0	0	5	2
Net current-period other comprehensive income	(59)	7	(33)	4
Ending balance	(714)	(562)	(714)	(562)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(86)	(94)	(107)	(90)
Other comprehensive income before reclassification	(56)	7	(35)	3
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net current-period other comprehensive income	(56)	7	(35)	3
Ending balance	(142)	(87)	(142)	(87)
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(569)	(476)	(572)	(476)
Other comprehensive income before reclassification	0	0	0	(1)
Amounts reclassified from accumulated other comprehensive loss	2	1	5	2
Net current-period other comprehensive income	2	1	5	1
Ending balance	(567)	(475)	(567)	(475)
Unrealized Income (Loss) on cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	0	1	(2)	0
Other comprehensive income before reclassification	(3)	0	(3)	0
Amounts reclassified from accumulated other comprehensive loss	(2)	(1)	0	0
Net current-period other comprehensive income	(5)	(1)	(3)	0
Ending balance	$ (5)	$ 0	$ (5)	$ 0

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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