Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in the carrying amount of goodwill
Balance at the beginning of the period	$ 1,842.6	$ 1,827.4	$ 1,724.8
Acquisitions	33.8	10.3	103.4
Disposal of businesses			(1.0)
Effect of foreign currency translation	(5.6)	4.9	0.2
Balance at the end of the period	1,870.8	1,842.6	1,827.4
Accumulated impairment losses	0.0
Goodwill, tax deductible amount	685.4
2018 Acquisitions
Change in the carrying amount of goodwill
Goodwill, tax deductible amount	$ 21.3
2016 Acquisitions
Change in the carrying amount of goodwill
Balance at the beginning of the period		$ 104.7
Balance at the end of the period			104.7
Goodwill, tax deductible amount			$ 104.7