Income Taxes - Income Tax (Benefit) Provision from Continuing Operations (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Pretax (loss) income:
U.S.	$ (593.4)	$ (127.3)	$ (279.3)
Foreign	797.9	864.6	369.1
Income before income taxes	204.5	737.3	89.8
Current (benefit) expense:
U.S. Federal	(98.0)	369.4	21.3
State	(5.3)	0.5	1.0
Foreign	14.1	60.8	23.8
Total current (benefit) expense	(89.2)	430.7	46.1
Deferred expense (benefit):
U.S. Federal	11.9	82.5	(114.7)
State	0.6	0.1	(5.4)
Foreign	(74.7)	(31.4)	(6.8)
Total deferred (benefit) expense	(62.2)	51.2	(126.9)
Total Income tax (benefit) provision	(151.4)	481.9	(80.8)
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Computed expected income tax provision	43.0	232.6	31.4
State income taxes, net of federal benefit	(8.7)	(1.3)	(4.6)
Foreign income taxed at lower than the federal rate	(94.0)	(208.8)	(105.0)
Impact of the Act - one-time transition tax, net of foreign tax credits	13.1	653.7	0.0
Impact of the Act - deferred tax effects, net of valuation allowance	0.0	(136.7)	0.0
Global intangible low-taxed income	95.4	0.0	0.0
Business realignment	(90.6)	0.0	0.0
Increases related to current year tax positions	9.0	32.0	53.7
Decreases related to prior year tax positions	(75.1)	(11.3)	(36.3)
Share-based compensation	(13.3)	(27.2)	(25.0)
Research and development tax credits	(27.5)	(17.0)	(12.8)
Intercompany prepaid tax asset amortization	5.2	7.4	7.9
Foreign exchange	4.6	(20.5)	(1.7)
Other	(2.6)	(0.5)	9.8
Change in valuation allowance	(9.9)	(20.5)	1.8
Total Income tax (benefit) provision	$ (151.4)	$ 481.9	$ (80.8)
Increase of basic net income per share due to release of prior year tax positions (in dollars per share)	$ 0.32	$ 0.05	$ 0.17
Increase of diluted net income per share due to release of prior year tax positions (in dollars per share)	$ 0.30	$ 0.05	$ 0.15
Income tax holiday, aggregate dollar amount	$ 0.1	$ 6.2	$ 13.2
Income tax holiday, benefits per share, basic		$ 0.03	$ 0.06
Income tax holiday, benefits per share, diluted		$ 0.02	$ 0.06