Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 436.0	$ 398.5	$ 220.7
Increases related to acquisitions	329.7	0.0	193.3
Decreases related to settlements with tax authorities	(8.3)	(0.1)	(11.7)
Decreases related to statute of limitation expirations	(16.2)	(10.9)	(7.6)
Increases related to current year tax positions	27.8	30.3	26.3
Decreases related to prior year tax positions	(5.6)		(22.5)
Increases related to prior year tax positions		18.2
Ending balance	763.4	436.0	398.5
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Unrecognized tax benefits, income tax penalties accrued	88.1	80.8
Unrecognized tax benefits, income tax penalties and interest expense	37.5	5.4	$ 5.8
Unrecognized tax benefits that would impact effective tax rate	664.4	$ 436.0
Unrecognized tax benefits, potential decrease	$ 50.0

Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

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Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of statutory penalties accrued for a tax position claimed or expected to be claimed by the entity, in its tax return.

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Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Amount of increase in unrecognized tax benefits resulting from acquisitions.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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