Accumulated Other Comprehensive Loss - Schedule of Changes in the Components of AOCI (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Changes in the components of AOCI
Beginning balance	$ 5,519.9	$ 5,337.1	$ 5,501.3	$ 5,585.5	$ 5,337.1	$ 5,585.5
Other comprehensive income, net of tax effect	1.8	0.0	0.2	0.5	1.8	0.7
Ending balance	5,702.9	5,519.9	5,443.7	5,501.3	5,702.9	5,443.7
Total
Changes in the components of AOCI
Beginning balance	(26.2)	(26.2)	(21.1)	(21.6)	(26.2)	(21.6)
Other comprehensive (loss) income before reclassifications					0.6
Reclassification of realized transactions					1.2
Other comprehensive income, net of tax effect	1.8	0.0	0.2	0.5	1.8
Ending balance	(24.4)	(26.2)	$ (20.9)	$ (21.1)	(24.4)	$ (20.9)
Minimum Pension Liability
Changes in the components of AOCI
Beginning balance		(13.4)			(13.4)
Other comprehensive (loss) income before reclassifications					0.7
Reclassification of realized transactions					1.2
Other comprehensive income, net of tax effect					1.9
Ending balance	(11.5)				(11.5)
Foreign Currency
Changes in the components of AOCI
Beginning balance		$ (12.8)			(12.8)
Other comprehensive (loss) income before reclassifications					(0.1)
Reclassification of realized transactions					0.0
Other comprehensive income, net of tax effect					(0.1)
Ending balance	$ (12.9)				$ (12.9)