Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill
Goodwill	$ 4,908.7	$ 4,945.5	$ 4,894.4
Current year acquisitions/(dispositions)	(0.2)	24.0
Foreign currency and other	(36.6)	27.1
IAN
Goodwill
Goodwill	4,231.6	4,264.5	4,218.1
Current year acquisitions/(dispositions)	(0.2)	23.5
Foreign currency and other	(32.7)	22.9
DXTRA
Goodwill
Goodwill	677.1	681.0	$ 676.3
Current year acquisitions/(dispositions)	0.0	0.5
Foreign currency and other	$ (3.9)	$ 4.2

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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