Shareowners' Equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,617.5	$ 2,663.6	$ 1,990.1
Other comprehensive income (loss) before reclassifications	(590.5)	146.7	260.0
Amounts reclassified from accumulated other comprehensive loss	44.4	90.6	99.6
Other comprehensive (loss) income	(546.1)	237.3	359.6
Ending balance	404.2	1,617.5	2,663.6
Total accumulated other comprehensive loss, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(941.9)	(1,179.2)	(1,538.8)
Other comprehensive (loss) income	(1,488.0)
Ending balance	(1,488.0)	(941.9)	(1,179.2)
Pension and other postretirement benefit plan adjustments, net of tax (Note 13)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(658.1)	(927.0)	(1,239.8)
Other comprehensive income (loss) before reclassifications	(532.1)	188.4	215.2
Amounts reclassified from accumulated other comprehensive loss	56.5	80.5	97.6
Other comprehensive (loss) income	(475.6)	268.9	312.8
Ending balance	(1,133.7)	(658.1)	(927.0)
Accumulated currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(286.0)	(237.7)	(294.9)
Other comprehensive income (loss) before reclassifications	(55.3)	(48.3)	57.2
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0
Other comprehensive (loss) income	(55.3)	(48.3)	57.2
Ending balance	(341.3)	(286.0)	(237.7)
Net unrealized gains (losses) on cash flow hedges, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	4.4	(14.4)	(4.1)
Other comprehensive income (loss) before reclassifications	(5.3)	8.7	(12.3)
Amounts reclassified from accumulated other comprehensive loss	(12.1)	10.1	2.0
Other comprehensive (loss) income	(17.4)	18.8	(10.3)
Ending balance	(13.0)	4.4	(14.4)
Net unrealized gains (losses) on available-for-sale investments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2.2)	(0.1)	0.0
Other comprehensive income (loss) before reclassifications	2.2	(2.1)	(0.1)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0
Other comprehensive (loss) income	2.2	(2.1)	(0.1)
Ending balance	$ 0.0	$ (2.2)	$ (0.1)

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

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

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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