Shareowners' Equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	$ 1,346.8	$ 404.2	$ 1,617.5
Other comprehensive income (loss)	596.4	16.5	(546.1)
End of period	2,694.1	1,346.8	404.2
Total accumulated other comprehensive loss, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(1,614.2)	(1,488.0)	(941.9)
Other comprehensive income (loss) before reclassifications	441.1	(81.5)	(590.5)
Amounts reclassified from accumulated other comprehensive loss	156.0	98.3	44.4
Other comprehensive income (loss)	597.1	16.8	(546.1)
End of period	(1,017.1)	(1,614.2)	(1,488.0)
Pension and other postretirement benefit plan adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(1,271.2)	(1,133.7)	(658.1)
Other comprehensive income (loss) before reclassifications	438.9	(100.2)	(532.1)
Amounts reclassified from accumulated other comprehensive loss	138.2	109.5	56.5
Other comprehensive income (loss)	577.1	9.3	(475.6)
End of period	(694.1)	(1,271.2)	(1,133.7)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(311.5)	(341.3)	(286.0)
Other comprehensive income (loss) before reclassifications	31.4	26.0	(55.3)
Other comprehensive income (loss)	31.4	26.0	(55.3)
End of period	(280.1)	(311.5)	(341.3)
Accumulated gain (loss), net, cash flow hedge, parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(31.5)	(13.0)	4.4
Other comprehensive income (loss) before reclassifications	(29.2)	(7.3)	(5.3)
Amounts reclassified from accumulated other comprehensive loss	17.8	(11.2)	(12.1)
Other comprehensive income (loss)	(11.4)	(18.5)	(17.4)
End of period	(42.9)	(31.5)	(13.0)
Net unrealized gains (losses) on available-for-sale investments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	0.0	0.0	(2.2)
Other comprehensive income (loss) before reclassifications		0.0	2.2
Other comprehensive income (loss)	0.0	0.0	2.2
End of period	$ 0.0	0.0	0.0
Cumulative Effect, Period of Adoption, Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period		2.2	6.1
End of period			2.2
Cumulative Effect, Period of Adoption, Adjustment [Member] | Total accumulated other comprehensive loss, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period		(146.8)
End of period			(146.8)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Pension and other postretirement benefit plan adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period		(146.8)
End of period			(146.8)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period		3.8
End of period			3.8
Cumulative Effect, Period of Adoption, Adjustment [Member] | Total accumulated other comprehensive loss, including non-controlling interest, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period		$ (143.0)
End of period			$ (143.0)