Goodwill and Other Intangible Assets - Schedule of Changes in the Carrying Value of Goodwill by Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill gross	$ 2,595.6	$ 2,578.6	$ 2,976.2
Accumulated impairment losses	(2,185.0)	(2,174.1)	(2,570.3)
Goodwill	410.6	404.5	405.9
Foreign exchange and other adjustments	(6.1)	(1.3)
Business Services
Goodwill [Line Items]
Goodwill gross	2,076.1	2,059.1	2,456.6
Accumulated impairment losses	(1,930.9)	(1,920.0)	(2,316.2)
Goodwill	145.2	139.1	140.4
Foreign exchange and other adjustments	(6.1)	(1.3)
Marketing Solutions
Goodwill [Line Items]
Goodwill gross	519.5	519.5	519.6
Accumulated impairment losses	(254.1)	(254.1)	(254.1)
Goodwill	$ 265.4	$ 265.4	$ 265.5