Derivative Instruments and Hedging Activities (Forward Contracts Effect on Statement of Operations and Comprehensive Income) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Total direct operating expense on consolidated statements of operations		$ 499.4	$ 463.2	$ 1,067.4	$ 993.2
Total interest expense on consolidated statements of operations	[1]	48.0	38.8	97.0	74.2
Direct operating | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in direct operating expense		0.0	0.0	0.0	(0.7)
Forward exchange contracts | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in accumulated other comprehensive income (loss)		0.0	0.4	0.0	0.4
Gain reclassified from accumulated other comprehensive income (loss) into direct operating expense		0.4	0.1	1.6	0.2
Interest rate swap agreements | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in accumulated other comprehensive income (loss)		(20.9)	12.2	(66.7)	5.4
Loss reclassified from accumulated other comprehensive income (loss) into interest expense		$ (2.7)	$ (2.9)	$ (4.4)	$ (3.9)

[1] Represents interest expense before interest on dissenting shareholders' liability.