Business Segment Information (Reconciliation of Operating Income) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Operating income	$ 548.5	$ 577.2	$ 1,087.6	$ 1,138.2
Facility closure	(23.2)	0.0	(23.2)	0.0
Gain on exchange with joint venture partner	36.8	0.0	36.8	0.0
Company headquarters relocation income (expense)	0.0	33.8	0.0	33.8
Segment Total
Segment Reporting Information [Line Items]
Operating income	534.9	543.4	1,074.0	1,104.4
Segment Reconciling Items
Segment Reporting Information [Line Items]
Facility closure	(23.2)	0.0	(23.2)	0.0
Gain on exchange with joint venture partner	36.8	0.0	36.8	0.0
Company headquarters relocation income (expense)	$ 0.0	$ 33.8	$ 0.0	$ 33.8

Net gain (loss) resulting from an exchange of equity affiliate investments.

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- Definition

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, excluding oil and gas property and timber property.

+ References

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Amount of gain (loss) from the difference between the sale price or salvage price and the book value of an asset that was sold or retired, and gain (loss) from the write down of assets from their carrying value to fair value.

+ References

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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