STOCK-BASED COMPENSATION: Stock-based compensation activity, by award type (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based compensation
Total non-cash stock-based compensation	$ 64.6	$ 72.3
Total non-cash stock-based compensation included in the consolidated statements of equity	44.9	49.0
Stock options
Share-based compensation
Share-based compensation expense	1.9	2.8
Restricted stock units
Share-based compensation
Share-based compensation expense	40.5	40.5
Arbor Holdback Agreement | Arbor
Share-based compensation
Share-based compensation expense	0.0	2.6
Consideration Holdback | Data Plus Math Corporation
Share-based compensation
Share-based compensation expense	6.0	4.1
Pacific Data Partners, LLC Agreement Plan | Pacific Data Partners LLC
Share-based compensation
Share-based compensation expense	13.8	21.4
Acuity Performance Earnout | Acuity Data
Share-based compensation
Share-based compensation expense	1.4	0.0
Liability-based equity awards
Share-based compensation
Total non-cash stock-based compensation	(19.7)	(23.3)
Other stock-based compensation
Share-based compensation
Share-based compensation expense	$ 1.0	$ 0.9