CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common Stock and Additional Paid-in-Capital	Common Stock Held in Treasury	Accumulated Other Comprehensive Loss	Retained Earnings
Balance, common stock shares issued (in shares) at Mar. 31, 2020		258,400,000
Beginning balance at Mar. 31, 2020	$ 5,585.5	$ 2,675.3	$ (500.6)	$ (21.6)	$ 3,432.4
Balance, common stock held in treasury (in shares) at Mar. 31, 2020			13,100,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	123.6				123.6
Other comprehensive income	0.5			0.5
Proceeds from sales of common stock through employee equity incentive plans (shares)		600,000
Proceeds from sales of common stock through employee equity incentive plans	11.0	$ 11.0
RSU and SAR withholdings (shares)		(100,000)
RSU and SAR withholdings	(11.0)	$ (11.0)
Treasury stock used for new issuances (shares)		(500,000)	(500,000)
Treasury stock used for new issuances	0.0	$ (14.8)	$ 14.8
Shares issued to settle convertible debt (in shares)		6,600,000
Shares issued to settle convertible debt	651.5	$ 651.5
Settlement of convertible debt	(810.7)	(810.7)
Share-based compensation	41.3	$ 41.3
Cash dividend	(90.4)				(90.4)
Balance, common stock shares issued (in shares) at Jun. 30, 2020		265,000,000.0
Ending balance at Jun. 30, 2020	$ 5,501.3	$ 2,542.6	$ (485.8)	(21.1)	3,465.6
Balance, common stock held in treasury (in shares) at Jun. 30, 2020			12,600,000
Balance, common stock shares issued (in shares) at Mar. 31, 2021	284,479,079	284,500,000
Beginning balance at Mar. 31, 2021	$ 5,337.1	$ 2,403.6	$ (433.8)	(26.2)	3,393.5
Balance, common stock held in treasury (in shares) at Mar. 31, 2021	10,950,485		11,000,000.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 252.8				252.8
Other comprehensive income	0.0			0.0
Proceeds from sales of common stock through employee equity incentive plans (shares)		800,000
Proceeds from sales of common stock through employee equity incentive plans	12.2	$ 12.2
RSU and SAR withholdings (shares)		(200,000)
RSU and SAR withholdings	(25.3)	$ (25.3)
Treasury stock used for new issuances (shares)		(600,000)	(600,000)
Treasury stock used for new issuances	0.0	$ (16.3)	$ 16.3
Share-based compensation	56.2	$ 56.2
Cash dividend	$ (113.1)				(113.1)
Balance, common stock shares issued (in shares) at Jun. 30, 2021	284,479,079	284,500,000
Ending balance at Jun. 30, 2021	$ 5,519.9	$ 2,430.4	$ (417.5)	$ (26.2)	$ 3,533.2
Balance, common stock held in treasury (in shares) at Jun. 30, 2021	10,438,935		10,400,000