Share-Based Compensation - Equity Incentive Plans, Stock Options Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Number of Shares
Outstanding at beginning of period (in shares)	149,010	281,882	284,340
Assumed upon acquisition (in shares)			141,751
Exercised (in shares)	(77,884)	(130,419)	(140,118)
Forfeited or expired (in shares)	(629)	(2,453)	(4,091)
Outstanding at end of period (in shares)	70,497	149,010	281,882
Weighted Average Exercise Price per Share
Outstanding at beginning of period (in dollars per share)	$ 31.59	$ 30.16	$ 31.21
Assumed upon acquisition (in dollars per share)			25.86
Exercised (in dollars per share)	31.48	28.71	27.67
Forfeited or expired (in dollars per share)	19.47	20.02	39.62
Outstanding at end of period (in dollars per share)	31.81	$ 31.59	$ 30.16
Share price (in dollars per share)	$ 155.22
Weighted average remaining contractual term	2 years 21 days
Employee Stock Option
Weighted Average Exercise Price per Share
Total intrinsic value of options exercised related to stock incentive plans	$ 6.5	$ 8.4	$ 8.3
Aggregate intrinsic value of options outstanding related to stock incentive plans	$ 10.9
Weighted average exercise price per share of exercisable options (in dollars per share)	$ 31.81	$ 31.59
Share-based compensation arrangement by share-based payment award, options, grants in period, grant date intrinsic value (in shares)	$ 0	$ 0	$ 0
Exercisable number of option shares (in shares)	70,497	149,010