Goodwill and Intangible Assets - Summary of Change in Goodwill (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 3,864.3
Purchase accounting reclassifications	0.9
Current period reclassification	1.9
Foreign currency translation	(124.5)
Goodwill, ending balance	3,742.6
Operating Segments | Insurance
Goodwill [Roll Forward]
Goodwill, beginning balance	998.8
Purchase accounting reclassifications	2.9
Current period reclassification	21.4
Foreign currency translation	(25.4)
Goodwill, ending balance	997.7
Operating Segments | Energy and Specialized Markets
Goodwill [Roll Forward]
Goodwill, beginning balance	2,389.5
Purchase accounting reclassifications	(1.8)
Current period reclassification	(19.5)
Foreign currency translation	(98.1)
Goodwill, ending balance	2,270.1
Operating Segments | Financial Services
Goodwill [Roll Forward]
Goodwill, beginning balance	476.0
Purchase accounting reclassifications	(0.2)
Current period reclassification	0.0
Foreign currency translation	(1.0)
Goodwill, ending balance	$ 474.8