Shareowners' Equity - Schedule of Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	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
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales	$ 1,570.0	$ 1,394.0	$ 1,681.3	$ 1,684.5	$ 1,730.2	$ 1,665.1	$ 1,657.2	$ 1,642.3	$ 6,329.8	$ 6,694.8	$ 6,666.0
Cost of sales									(3,734.6)	(3,794.7)	(3,781.1)
Selling, general and administrative expenses									(1,479.8)	(1,538.5)	(1,587.9)
Interest expense									(103.5)	(98.2)	(73.0)
Income before income taxes									1,136.1	901.0	1,330.8
Income tax provision									(112.9)	(205.2)	(795.3)
Net income	$ 262.7	$ 317.8	$ 132.2	$ 310.7	$ 8.1	$ 261.4	$ 346.0	$ 80.3	1,023.4	695.8	535.5
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income									98.3	44.4	90.6
Amortization of prior service credit | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales and selling, general and administrative expenses									(4.5)	(4.2)	(4.9)
Amortization of net actuarial loss | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales and selling, general and administrative expenses									148.7	78.7	115.1
Settlements | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of sales and selling, general and administrative expenses									0.0	1.2	0.7
Pension and other postretirement benefit plan adjustments, net of tax | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes									144.2	75.7	110.9
Income tax provision									(34.7)	(19.2)	(30.4)
Net income									109.5	56.5	80.5
Net unrealized gains (losses) on cash flow hedges, net of tax | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Sales									0.7	(1.0)	(2.4)
Cost of sales									(19.6)	(18.2)	17.2
Selling, general and administrative expenses									1.4	1.3	(1.2)
Interest expense									2.1	1.2	0.0
Income before income taxes									(15.4)	(16.7)	13.6
Income tax provision									4.2	4.6	(3.5)
Net income									$ (11.2)	$ (12.1)	$ 10.1