Stock-Based Compensation Plans (Other Information Pertaining to RSUs) (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		May 31, 2020	May 31, 2019	May 31, 2018
Time-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value per share		$ 73.28	$ 62.20	$ 51.15
Weighted-average remaining vesting period (years)		2 years 10 months 24 days	2 years 10 months 24 days	3 years 2 months 12 days
Total intrinsic value of RSUs vested		$ 40.0	$ 1.2	$ 60.9
Aggregate intrinsic value of nonvested RSUs	[1]	99.9	127.0	69.2
Total grant-date fair value of RSUs vested		$ 23.6	$ 0.8	$ 42.4
Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value per share	[2],[3]	$ 80.59
Weighted-average remaining vesting period (years)	[3]	2 years 1 month 6 days
Aggregate intrinsic value of nonvested RSUs	[1],[3]	$ 4.4

[1] Based on the market price of the underlying common stock as of May 31, 2020, 2019 and 2018.

[2] For performance-based RSUs, granted number assumes achievement of performance goals at target. Actual number of shares to be earned may differ from this amount.

[3] No performance-based RSUs were granted during fiscal 2019 and fiscal 2018.