Shareowners' Equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	$ 3,675.0	$ 3,743.0	$ 3,016.0
Other comprehensive (loss) income before reclassifications	93.0	28.0	64.0
Amounts reclassified from accumulated other comprehensive loss	22.0	(10.0)	64.0
Other comprehensive income	115.0	18.0	128.0
End of period	3,711.0	3,675.0	3,743.0
Total accumulated other comprehensive loss, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(772.0)	(790.0)	(918.0)
Other comprehensive income	115.0	18.0	128.0
End of period	(657.0)	(772.0)	(790.0)
Pension and other postretirement benefit plan adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(431.0)	(408.0)	(448.0)
Other comprehensive (loss) income before reclassifications	73.0	(23.0)	(50.0)
Amounts reclassified from accumulated other comprehensive loss	23.0	0.0	90.0
Other comprehensive income	96.0	(23.0)	40.0
End of period	(335.0)	(431.0)	(408.0)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(297.0)	(365.0)	(465.0)
Other comprehensive (loss) income before reclassifications	16.0	66.0	100.0
Amounts reclassified from accumulated other comprehensive loss	0.0	2.0	0.0
Other comprehensive income	16.0	68.0	100.0
End of period	(281.0)	(297.0)	(365.0)
Accumulated currency translation adjustments, net of tax | Currency Swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income	17.0
Accumulated gain (loss), net, cash flow hedge, parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(44.0)	(17.0)	(5.0)
Other comprehensive (loss) income before reclassifications	4.0	(15.0)	14.0
Amounts reclassified from accumulated other comprehensive loss	(1.0)	(12.0)	(26.0)
Other comprehensive income	3.0	(27.0)	(12.0)
End of period	$ (41.0)	$ (44.0)	$ (17.0)