Accumulated Other Comprehensive Loss - Schedule of Changes in the Components of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Changes in the components of AOCI
Beginning balance	$ 5,585.5	$ 5,287.5	$ 3,279.8
Other comprehensive (loss) income before reclassifications	(5.7)	(0.4)
Reclassification of realized transactions	1.1	0.8
Other comprehensive (loss) income, net of tax effect	(4.6)	0.4	(1.4)
Ending balance	5,337.1	5,585.5	5,287.5
Total
Changes in the components of AOCI
Beginning balance	(21.6)	(20.7)	(17.6)
Other comprehensive (loss) income, net of tax effect	(4.6)	0.4	(1.4)
Ending balance	(26.2)	(21.6)	(20.7)
Total \| Cumulative Effect, Period of Adoption, Adjustment
Changes in the components of AOCI
Beginning balance		(1.3)
Ending balance			(1.3)
Total \| Cumulative Effect, Period of Adoption, Adjusted Balance
Changes in the components of AOCI
Beginning balance		(22.0)
Ending balance			(22.0)
Unrealized Holding Gains (Losses) Available-for-sale Securities
Changes in the components of AOCI
Beginning balance	0.0	0.2
Other comprehensive (loss) income before reclassifications	0.0	0.0
Reclassification of realized transactions	0.0	0.0
Other comprehensive (loss) income, net of tax effect	0.0	0.0
Ending balance	0.0	0.0	0.2
Unrealized Holding Gains (Losses) Available-for-sale Securities \| Cumulative Effect, Period of Adoption, Adjustment
Changes in the components of AOCI
Beginning balance		(0.2)
Ending balance			(0.2)
Unrealized Holding Gains (Losses) Available-for-sale Securities \| Cumulative Effect, Period of Adoption, Adjusted Balance
Changes in the components of AOCI
Beginning balance		0.0
Ending balance			0.0
Minimum Pension Liability
Changes in the components of AOCI
Beginning balance	(5.1)	(6.2)
Other comprehensive (loss) income before reclassifications	(9.4)	1.4
Reclassification of realized transactions	1.1	0.8
Other comprehensive (loss) income, net of tax effect	(8.3)	2.2
Ending balance	(13.4)	(5.1)	(6.2)
Minimum Pension Liability \| Cumulative Effect, Period of Adoption, Adjustment
Changes in the components of AOCI
Beginning balance		(1.1)
Ending balance			(1.1)
Minimum Pension Liability \| Cumulative Effect, Period of Adoption, Adjusted Balance
Changes in the components of AOCI
Beginning balance		(7.3)
Ending balance			(7.3)
Foreign Currency
Changes in the components of AOCI
Beginning balance	(16.5)	(14.7)
Other comprehensive (loss) income before reclassifications	3.7	(1.8)
Reclassification of realized transactions	0.0	0.0
Other comprehensive (loss) income, net of tax effect	3.7	(1.8)
Ending balance	$ (12.8)	(16.5)	(14.7)
Foreign Currency \| Cumulative Effect, Period of Adoption, Adjustment
Changes in the components of AOCI
Beginning balance		0.0
Ending balance			0.0
Foreign Currency \| Cumulative Effect, Period of Adoption, Adjusted Balance
Changes in the components of AOCI
Beginning balance		$ (14.7)
Ending balance			$ (14.7)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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