Accumulated Other Comprehensive Income (Loss) (Tables)

12 Months Ended

Sep. 30, 2021

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

Schedule of changes in accumulated other comprehensive income (loss) by component

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

(in millions)	Currency Translation Adjustments		Unrealized Losses on Defined Benefit Plans		Unrealized Gains on Investments		Total
as of and for the fiscal years ended September 30, 2021, 2020 and 2019
Balance at October 1, 2018	$	(372.9)	$	(4.2)	$	6.5	$	(370.6)
Adoption of new accounting guidance	—		—		(8.0)		(8.0)
Other comprehensive income (loss)
Other comprehensive loss before reclassifications, net of tax	(53.9)		(2.4)		(5.4)		(61.7)
Reclassifications to compensation and benefits expense, net of tax	—		0.4		—		0.4
Reclassifications to net investment and other income (losses), net of tax	1.4		—		6.9		8.3
Total other comprehensive income (loss)	(52.5)		(2.0)		1.5		(53.0)
Balance at September 30, 2019	$	(425.4)	$	(6.2)	$	—	$	(431.6)
Other comprehensive income (loss)
Other comprehensive income (loss) before reclassifications, net of tax	23.8		(2.1)		(1.3)		20.4
Reclassifications to compensation and benefits expense, net of tax	—		0.3		—		0.3
Reclassifications to net investment and other income (losses), net of tax	2.0		—		1.3		3.3
Total other comprehensive income (loss)	25.8		(1.8)		—		24.0
Balance at September 30, 2020	$	(399.6)	$	(8.0)	$	—	$	(407.6)
Other comprehensive income
Other comprehensive income before reclassifications, net of tax	27.1		1.6		—		28.7
Reclassifications to compensation and benefits expense, net of tax	—		(0.7)		—		(0.7)
Reclassifications to net investment and other income (losses), net of tax	2.0		—		—		2.0
Total other comprehensive income	29.1		0.9		—		30.0
Balance at September 30, 2021	$	(370.5)	$	(7.1)	$	—	$	(377.6)