Business Segment and Geographic Information (Reconciliation of Operating Income) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	May 01, 2019	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Change in inventory valuation method										$ 2,423.8	$ 2,289.5	$ 2,015.0
Facility closure									$ (29.0)	0.0	(29.0)	0.0
Cost reduction actions						$ 0.0	$ (25.5)	$ 0.0	0.0	0.0	(25.5)	0.0
Gain on exchange of equity affiliate investments	$ 29.1					0.0	29.1	0.0	0.0	0.0	29.1	0.0
Company headquarters relocation income (expense)		$ 0.0	$ 0.0	$ 33.8	$ 0.0					33.8	0.0	0.0
Operating income		$ 560.2	$ 539.2	$ 577.2	$ 561.0	$ 603.2	$ 569.7	$ 516.5	$ 455.0	2,237.6	2,144.4	1,965.6
Segment Reconciling Items
Segment Reporting Information [Line Items]
Facility closure										0.0	(29.0)	0.0
Cost reduction actions										0.0	(25.5)	0.0
Gain on exchange of equity affiliate investments										0.0	29.1	0.0
Company headquarters relocation income (expense)										33.8	0.0	0.0
Segment Total
Segment Reporting Information [Line Items]
Operating income										2,203.8	2,169.8	1,941.5
Change in Inventory Valuation Method | Segment Reconciling Items
Segment Reporting Information [Line Items]
Change in inventory valuation method										$ 0.0	$ 0.0	$ 24.1