Restructuring Accruals (Narrative) (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2018 USD ($) employee	Jun. 30, 2017 USD ($) employee	Jun. 30, 2016 USD ($) employee
Restructuring Cost and Reserve [Line Items]
Number of employees affected by the plan | employee					215	150
Restructuring charges	$ 3.1	$ 4.3	$ 8.1		$ 12.4	$ 10.3
Reversal of excess accrual				$ (0.8)
Restructuring liability		8.7		107.6	8.7
Restructuring liability, current portion				91.6
Restructuring liability, noncurrent portion				16.0
Restructuring, business acquisition and integration charges
Restructuring Cost and Reserve [Line Items]
Manuscript and art inventory write-down				0.5	0.2	0.5
Employee Terminations
Restructuring Cost and Reserve [Line Items]
Restructuring charges					11.9	9.8
Reversal of excess accrual				(0.8)	(1.8)	(3.2)
Restructuring liability		8.7		101.3	8.7	$ 7.4
Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Other restructuring costs					0.3
Reversal of excess accrual				0.0
Restructuring liability		$ 0.0		$ 6.3	$ 0.0
Restructuring related to 2018 performance improvement plan
Restructuring Cost and Reserve [Line Items]
Number of employees affected by the plan | employee				1,800
Restructuring related to 2018 performance improvement plan | Employee Terminations
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 104.9