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Restructuring Charges (Details) $ in Millions	3 Months Ended		9 Months Ended
Restructuring Charges (Details) $ in Millions	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Restructuring and Related Cost, Number of Positions Eliminated			627
Severance and termination costs			$ 22.0
Lease impairment cost			11.9
Restructuring charges	$ 0.0	$ 0.0	33.9	$ 0.0
Payments for Restructuring			(18.4)
Restructuring Reserve	$ 3.6		3.6		$ 0.0
IAN [Member]
Restructuring charges			27.6
CMG [Member]
Restructuring charges			$ 5.6