Shareowners' Equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	$ 404.2	$ 1,617.5	$ 2,663.6
Other comprehensive (loss) income	16.5	(546.1)	237.3
End of period	1,346.8	404.2	1,617.5
Total accumulated other comprehensive loss, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(1,488.0)	(941.9)	(1,179.2)
Other comprehensive income (loss) before reclassifications	(81.5)	(590.5)	146.7
Amounts reclassified from accumulated other comprehensive loss	98.3	44.4	90.6
Other comprehensive (loss) income	16.8	(546.1)	237.3
End of period	(1,614.2)	(1,488.0)	(941.9)
Pension and other postretirement benefit plan adjustments, net of tax (Note 14)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(1,133.7)	(658.1)	(927.0)
Other comprehensive income (loss) before reclassifications	(100.2)	(532.1)	188.4
Amounts reclassified from accumulated other comprehensive loss	109.5	56.5	80.5
Other comprehensive (loss) income	9.3	(475.6)	268.9
End of period	(1,271.2)	(1,133.7)	(658.1)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(341.3)	(286.0)	(237.7)
Other comprehensive income (loss) before reclassifications	26.0	(55.3)	(48.3)
Other comprehensive (loss) income	26.0	(55.3)	(48.3)
End of period	(311.5)	(341.3)	(286.0)
Net unrealized gains (losses) on cash flow hedges, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(13.0)	4.4	(14.4)
Other comprehensive income (loss) before reclassifications	(7.3)	(5.3)	8.7
Amounts reclassified from accumulated other comprehensive loss	(11.2)	(12.1)	10.1
Other comprehensive (loss) income	(18.5)	(17.4)	18.8
End of period	(31.5)	(13.0)	4.4
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	(2.2)	(0.1)
Other comprehensive income (loss) before reclassifications		2.2	(2.1)
Other comprehensive (loss) income	0.0	2.2	(2.1)
End of period	0.0	0.0	(2.2)
Adoption of accounting standard/other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	2.2	6.1
End of period		2.2	$ 6.1
Adoption of accounting standard/other | 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)
Adoption of accounting standard/other | 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)
Adoption of accounting standard/other | Pension and other postretirement benefit plan adjustments, net of tax (Note 14)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(146.8)
End of period		(146.8)
Adoption of accounting standard/other | 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