Goodwill - Changes in Carrying Value of Goodwill by Reportable Segment (Details) - USD ($)	3 Months Ended			12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Balance at beginning of period				$ 1,260,100,000	$ 1,297,100,000
Goodwill acquired during the period				0	48,000,000.0	$ 6,100,000
Goodwill allocated to business units sold/deconsolidated					(20,100,000)
Impairment charge	$ 0	$ 0	$ 0	(66,800,000)	(64,000,000.0)
Currency impact and other				32,500,000	(900,000)
Balance at end of period				1,225,800,000	1,260,100,000	1,297,100,000
Reportable segments | Americas
Goodwill [Roll Forward]
Balance at beginning of period				535,600,000	519,900,000
Goodwill acquired during the period					14,200,000
Currency impact and other				1,000,000.0	1,500,000
Balance at end of period				536,600,000	535,600,000	519,900,000
Reportable segments | Southern Europe
Goodwill [Roll Forward]
Balance at beginning of period				144,800,000	112,200,000
Goodwill acquired during the period					33,800,000
Currency impact and other				10,100,000	(1,200,000)
Balance at end of period				154,900,000	144,800,000	112,200,000
Reportable segments | Northern Europe
Goodwill [Roll Forward]
Balance at beginning of period				374,600,000	435,400,000
Impairment charge				(66,800,000)	(60,200,000)
Currency impact and other				18,800,000	(600,000)
Balance at end of period				326,600,000	374,600,000	435,400,000
Reportable segments | APME
Goodwill [Roll Forward]
Balance at beginning of period				79,100,000	102,000,000.0
Goodwill allocated to business units sold/deconsolidated					(18,500,000)
Impairment charge					(3,800,000)
Currency impact and other				2,600,000	(600,000)
Balance at end of period				81,700,000	79,100,000	102,000,000.0
Corporate
Goodwill [Roll Forward]
Balance at beginning of period				126,000,000.0	127,600,000
Goodwill allocated to business units sold/deconsolidated					(1,600,000)
Balance at end of period				$ 126,000,000.0	$ 126,000,000.0	$ 127,600,000