Shareowners' Equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	$ 3,743.4	$ 3,016.7	$ 2,694.1
Other comprehensive income	18.0	127.5	99.3
End of period	3,675.2	3,743.4	3,016.7
Total accumulated other comprehensive loss, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(790.1)	(917.5)	(1,017.1)
Other comprehensive income (loss) before reclassifications	27.7	63.2	37.0
Amounts reclassified from accumulated other comprehensive loss	(10.0)	64.2	62.6
Other comprehensive income	17.7	127.4	99.6
End of period	(772.4)	(790.1)	(917.5)
Pension and other postretirement benefit plan adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(407.1)	(447.8)	(694.1)
Other comprehensive income (loss) before reclassifications	(24.3)	(49.7)	170.7
Amounts reclassified from accumulated other comprehensive loss	0.4	90.4	75.6
Other comprehensive income	(23.9)	40.7	246.3
End of period	(431.0)	(407.1)	(447.8)
Accumulated gain (loss), net, cash flow hedge, parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(18.1)	(4.7)	(42.9)
Other comprehensive income (loss) before reclassifications	(14.6)	12.8	51.2
Amounts reclassified from accumulated other comprehensive loss	(12.4)	(26.2)	(13.0)
Other comprehensive income	(27.0)	(13.4)	38.2
End of period	(45.1)	(18.1)	(4.7)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(364.9)	(465.0)	(280.1)
Other comprehensive income (loss) before reclassifications	66.6	100.1	(184.9)
Amounts reclassified from accumulated other comprehensive loss	2.0
Other comprehensive income	68.6	100.1	(184.9)
End of period	$ (296.3)	$ (364.9)	$ (465.0)