Equity and Other Comprehensive Income (Loss) - Summary of Reclassification out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization and settlement recognition of net actuarial loss, included in pension cost		$ 8.5	$ 3.2	$ 17.2	$ 8.1
Amortization of prior service costs, Net of Tax		1.0	0.4	1.5	0.9
Reclassification of stranded tax effects	[1]			73.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax		2.5		1.2
Parent [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss, Pre-Tax Amount	[2],[3]	(11.5)	(4.1)	(23.1)	(10.7)
Amortization of net actuarial loss, Tax	[2],[3]	3.1	1.1	6.1	2.8
Amortization and settlement recognition of net actuarial loss, included in pension cost	[2],[3]	(8.4)	(3.0)	(17.0)	(7.9)
Amortization of prior service costs, Pre-Tax Amount	[2],[3]	(1.3)	(0.6)	(2.0)	(1.2)
Amortization of prior service costs, Tax	[2],[3]	0.3	0.2	0.5	0.3
Amortization of prior service costs, Net of Tax	[2],[3]	(1.0)	(0.4)	(1.5)	(0.9)
Defined Benefit Plans, before Tax	[2]	(12.8)	(4.7)	(25.1)	(11.9)
Defined Benefit Plans, Tax	[2]	3.4	1.3	80.0	3.1
Defined Benefit Plans, Net of Tax	[2]	(9.4)	(3.4)	54.9	(8.8)
Total Reclassifications From Other Comprehensive Income Before Tax	[2]	(16.2)	(4.7)	(26.7)	(11.9)
Total Reclassifications From Other Comprehensive Income Tax Portion	[2]	4.4	1.3	80.5	3.1
Total Reclassifications From Other Comprehensive Income Net of Tax	[2]	(11.8)	$ (3.4)	53.8	$ (8.8)
Parent [Member] | Cash Flow Hedges [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[2]	(3.4)		(1.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	[2]	1.0		0.5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	[2]	(2.4)		(1.1)
Parent [Member] | ASU 2018-02 [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Reclassification of stranded tax effects	[4]			73.4
Parent [Member] | Interest Rate Contract [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[2],[5]	0.3		1.0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	[2],[5]			(0.2)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	[2],[5]	0.3		0.8
Parent [Member] | Natural Gas Commodity Hedge [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[2],[6]	(3.7)		(2.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	[2],[6]	1.0		0.7
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	[2],[6]	$ (2.7)		$ (1.9)

[1] All amounts are net of tax and noncontrolling interests.

[2] Amounts in parentheses indicate charges to earnings. Amounts pertaining to noncontrolling interests are excluded.

[3] Included in the computation of net periodic pension cost. See “Note 5. Retirement Plans” for additional details.

[4] Amount reclassified to retained earnings as a result of the adoption of ASU 2018-02.

[5] These accumulated other comprehensive income components are included in interest expense, net.

[6] These accumulated other comprehensive income components are included in cost of goods sold.