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Business Combinations (Details) - USD ($)
$ in Millions
Apr. 06, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Business Acquisition [Line Items]        
Goodwill   $ 7,157.1 $ 6,590.7 $ 6,129.2
Guggenheim Investments' ETF Business        
Business Acquisition [Line Items]        
Consideration transferred in business acquisition $ 1,200.0      
Goodwill 626.0      
Fund Management Contracts | Guggenheim Investments' ETF Business        
Business Acquisition [Line Items]        
Intangible assets acquired $ 578.0