Debt - Settlement of debt (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended												12 Months Ended
	Feb. 29, 2024	Sep. 30, 2023	Aug. 31, 2023	Jun. 30, 2023	May 31, 2023	Aug. 31, 2022	May 31, 2022	Feb. 28, 2022	Dec. 31, 2021	Aug. 31, 2021	Jun. 30, 2021	Dec. 31, 2020	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Debt Instrument [Line Items]
Cash Paid													$ 3,400.0	$ 0.0	$ 1,000.0
Shares issued to settle convertible debt															670.7
Net Loss on Inducements and Settlements													$ 12.2	$ 8.3	$ 113.4
Maximum
Debt Instrument [Line Items]
Option indexed to equity, strike price (in dollars per share)												$ 116.79
Line of Credit | Long-term Debt | Revolving Credit Facility
Debt Instrument [Line Items]
Net Loss on Inducements and Settlements									$ 0.6
2015 Senior Convertible Debt | Senior Convertible Debt | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled					$ 5.6	$ 22.0			36.6	$ 70.4
Cash Paid					18.9	67.7			36.6	70.4
Shares issued to settle convertible debt									103.9	159.9
Total consideration					18.9	67.7			140.5	230.3
Net Loss on Inducements and Settlements					0.4	1.3			4.1	10.6
Fair Value Settled									36.2	71.0
Equity Component									104.2	158.9
2017 Senior Convertible Debt | Senior Convertible Debt | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled			$ 18.2		25.9	14.9	$ 31.0	$ 64.9	39.7	100.7
Cash Paid			42.7		56.3	29.2	65.3	64.9	39.7	100.7
Shares issued to settle convertible debt								74.6	61.4	123.5
Total consideration			42.7		56.3	29.2	65.3	139.5	101.1	224.2
Net Loss on Inducements and Settlements			$ 3.1		6.6	$ 0.8	5.9	11.8	6.3	31.5
Fair Value Settled								60.0	37.4	100.0
Equity Component								$ 75.5	63.0	113.0
2017 Junior Convertible Debt | Junior Convertible Debt | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled					6.5		3.6		19.9	92.5
Cash Paid					14.9		8.2		19.9	92.5
Shares issued to settle convertible debt									31.6	115.8
Total consideration					14.9		8.2		51.5	208.3
Net Loss on Inducements and Settlements					$ 2.1		$ 0.3		5.1	43.1
Fair Value Settled									15.7	87.7
Equity Component									$ 35.9	$ 116.6
2020 Senior Convertible Debt | Senior Convertible Debt
Debt Instrument [Line Items]
Capped options indexed to equity, costs												$ 35.8
4.333% 2023 Notes | Senior Indebtedness | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled				$ 1,000.0
Cash Paid				1,000.0
Total consideration				1,000.0
Net Loss on Inducements and Settlements				$ 0.0
2.670% 2023 Notes | Senior Indebtedness | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled		$ 1,000.0
Cash Paid		1,000.0
Total consideration		1,000.0
Net Loss on Inducements and Settlements		$ 0.0
0.972% 2024 Notes | Senior Indebtedness | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled	$ 1,400.0
Cash Paid	1,400.0
Total consideration	1,400.0
Net Loss on Inducements and Settlements	$ 0.0
3.922% 2021 Notes | Senior Indebtedness | Long-term Debt
Debt Instrument [Line Items]
Principal Amount Settled											$ 1,000.0
Cash Paid											1,000.0
Total consideration											1,000.0
Net Loss on Inducements and Settlements											$ 0.3