Income Taxes (Components of Deferred Income Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Jun. 30, 2020
Deferred tax assets:
Accrued expenses not currently deductible	$ 244.2	$ 203.0
Stock-based compensation expense	38.4	33.8
Foreign tax credits	21.3	20.1
Net operating losses	46.3	52.0
Retirement benefits	0.0	46.0
Other	34.7	25.9
Deferred tax assets, gross	384.9	380.8
Less: valuation allowances	(13.4)	(12.0)
Deferred tax assets, net	371.5	368.8
Deferred tax liabilities:
Deferred revenue	494.5	475.0
Fixed and intangible assets	119.4	288.2
Prepaid expenses	27.9	82.3
Prepaid retirement benefits	37.7	0.0
Unrealized investment gains, net	101.7	187.9
Tax on unrepatriated earnings	11.4	22.2
Other	13.6	6.4
Deferred tax liabilities	806.2	1,062.0
Net deferred tax liabilities	$ 434.7	$ 693.2