Funds Held for Clients and Corporate Investments (Realized Gains and Losses from Sale of Available-for-sale Securities) (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	May 31, 2019	[1]	Feb. 28, 2019	[1]	Nov. 30, 2018	[1]	Aug. 31, 2018	[1]	Feb. 28, 2018	[1],[2]	May 31, 2019	May 31, 2018		May 31, 2017
Funds Held for Clients and Corporate Investments [Abstract]
Gross realized gains											$ 0.6	$ 0.3		$ 0.1
Gross realized losses											$ (0.6)	(0.2)
Net realized gains	$ 0.1		$ 0.1		$ (0.3)		$ 0.1		$ 0.1			$ 0.1	[1],[2]	$ 0.1

[1] Total net realized gains/(losses) on the combined funds held for clients and corporate investment portfolios.

[2] Amounts have been adjusted to reflect the adoption of ASC Topic 606.