Share-Based Compensation - Equity Incentive Plans, Stock Options Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Option shares outstanding beginning balance (in shares)	284,340	433,117	913,508
Options assumed upon acquisition (in shares)	141,751
Options exercised (in shares)	(140,118)	(131,666)	(437,906)
Options forfeited or expired (in shares)	(4,091)	(17,111)	(42,485)
Option shares outstanding ending balance (in shares)	281,882	284,340	433,117
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Option shares outstanding beginning balance (in dollars per share)	$ 31.21	$ 31.51	$ 33.00
Options assumed upon acquisition (in dollars per share)	25.86
Options exercised (in dollars per share)	27.67	31.75	34.34
Options forfeited or expired (in dollars per share)	39.62	34.73	34.26
Option shares outstanding ending balance (in dollars per share)	$ 30.16	$ 31.21	$ 31.51
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Exercisable number of option shares (in shares)	278,591	224,022
Weighted average exercise price per share of exercisable options (in dollars per share)	$ 30.03	$ 29.96
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Total intrinsic value of options exercised related to stock incentive plans	$ 8.3	$ 7.4	$ 9.6
Aggregate intrinsic value of options outstanding related to stock incentive plans	14.9
Aggregate intrinsic value of options exercisable related to stock incentive plans	$ 14.8
Share-based compensation arrangement by share-based payment award, options, grants in period, grant date intrinsic value	$ 0	$ 0	$ 0