Accumulated Other Comprehensive Income (Loss)

12 Months Ended

Dec. 31, 2023

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Accumulated Other Comprehensive Income (Loss)

21. Accumulated Other Comprehensive Income (Loss)

Changes in accumulated other comprehensive income (loss) by component were as follows (in millions):

	Employee Pension and Postretirement Benefits, Net of Tax			Cumulative Translation Adjustments			Derivative Instruments, Net of Tax			Accumulated Other Comprehensive Income (Loss)
Balance at September 30, 2020	$	(95.9	)	$	(102.1	)	$	(0.4	)	$	(198.4	)
Other comprehensive income (loss) before reclassifications		57.1			3.8			1.5			62.4
Amounts reclassified from accumulated other comprehensive income (loss)		4.6			—			0.4			5.0
Net current period other comprehensive income (loss)		61.7			3.8			1.9			67.4
Balance at September 30, 2021		(34.2	)		(98.3	)		1.5			(131.0	)
Other comprehensive income (loss) before reclassifications		8.2			(6.9	)		0.9			2.2
Amounts reclassified from accumulated other comprehensive income (loss)		0.4			—			(0.2	)		0.2
Net current period other comprehensive income (loss)		8.6			(6.9	)		0.7			2.4
Balance at December 31, 2021		(25.6	)		(105.2	)		2.2			(128.6	)
Other comprehensive income (loss) before reclassifications		29.3			(31.0	)		6.2			4.5
Amounts reclassified from accumulated other comprehensive income (loss)		27.4			4.6			(0.2	)		31.8
Net current period other comprehensive income (loss)		56.7			(26.4	)		6.0			36.3
Balance at December 31, 2022		31.1			(131.6	)		8.2			(92.3	)
Other comprehensive income (loss) before reclassifications		3.5			24.2			(0.5	)		27.2
Amounts reclassified from accumulated other comprehensive income (loss)		(1.6	)		2.9			(8.2	)		(6.9	)
Net current period other comprehensive income (loss)		1.9			27.1			(8.7	)		20.3
Balance at December 31, 2023	$	33.0		$	(104.5	)	$	(0.5	)	$	(72.0	)

Reclassifications out of accumulated other comprehensive income (loss) included in the computation of net periodic pension and postretirement benefit cost (See Note 6 for additional details regarding employee benefit plans) were as follows (in millions):

	Classification of	Year Ended December 31,						(transition period) Three Months Ended December 31,			Year Ended September 30,
	income (expense)	2023			2022			2021			2021
Amortization of employee pension and postretirement benefits items
Prior service costs	Miscellaneous, net	$	0.5		$	0.8		$	0.2		$	0.9
Settlement	Miscellaneous, net		—			33.6			—			—
Actuarial (gains) losses	Miscellaneous, net		(2.6	)		1.3			0.3			5.2
Total before tax			(2.1	)		35.7			0.5			6.1
Tax benefit			0.5			(8.3	)		(0.1	)		(1.5	)
Net of tax		$	(1.6	)	$	27.4		$	0.4		$	4.6