Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill
Goodwill	$ 4,894.4	$ 4,875.9	$ 3,820.4
Current year acquisitions	2.8	1,132.0
Foreign currency and other	15.7	(76.5)
IAN
Goodwill
Goodwill	4,225.8	4,209.3	3,161.8
Current year acquisitions	2.1	1,112.0
Foreign currency and other	14.4	(64.5)
CMG
Goodwill
Goodwill	668.6	666.6	$ 658.6
Current year acquisitions	0.7	20.0
Foreign currency and other	$ 1.3	$ (12.0)

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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