Restructuring Charges Segments (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 47.3	$ 0.0	$ 159.9	$ 33.9
Lease impairment costs	26.6	$ 0.0	92.3	$ 11.9
IAN [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	24.9		93.7
Lease impairment costs	14.3		50.1
CMG [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	17.2		53.9
Lease impairment costs	$ 12.8		$ 39.6

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration