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, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss, Net of Tax		$ 1.5	$ 5.8	$ 2.8	$ 11.4
Amortization of prior service costs, Net of Tax		1.5	1.0	2.9	2.1
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax			1.4		2.9
Parent [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amortization of net actuarial loss, Pre-Tax Amount	[1],[2]	(1.9)	(7.4)	(3.5)	(14.8)
Amortization of net actuarial loss, Tax	[1],[2]	0.5	1.7	0.9	3.6
Amortization of net actuarial loss, Net of Tax	[1],[2]	(1.4)	(5.7)	(2.6)	(11.2)
Amortization of prior service costs, Pre-Tax Amount	[1],[2]	(1.9)	(1.3)	(3.8)	(2.8)
Amortization of prior service costs, Tax	[1],[2]	0.5	0.3	1.0	0.7
Amortization of prior service costs, Net of Tax	[1],[2]	(1.4)	(1.0)	(2.8)	(2.1)
Defined Benefit Plans, before Tax	[1]	(3.8)	(8.7)	(7.3)	(17.6)
Defined Benefit Plans, Tax	[1]	1.0	2.0	1.9	4.3
Defined Benefit Plans, Net of Tax	[1]	(2.8)	(6.7)	(5.4)	(13.3)
Total Reclassifications From Other Comprehensive Income Before Tax	[1]	(3.8)	(10.6)	(7.3)	(21.5)
Total Reclassifications From Other Comprehensive Income Tax Portion	[1]	1.0	2.5	1.9	5.3
Total Reclassifications From Other Comprehensive Income Net of Tax	[1]	$ (2.8)	(8.1)	$ (5.4)	(16.2)
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	[1],[3]		(1.9)		(3.9)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	[1],[3]		0.5		1.0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	[1],[3]		$ (1.4)		$ (2.9)

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

[2] Included in the computation of net periodic pension cost. See “Note 4. Retirement Plans” for additional details.

[3] These accumulated other comprehensive income components are included in Interest expense, net.