Segment Information Balance Sheet (Details) - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Segments:    
Assets $ 11,697.9 $ 12,485.2
IAN    
Segments:    
Assets 10,324.9 10,660.0
CMG    
Segments:    
Assets 1,379.7 1,428.3
Corporate and Other    
Segments:    
Assets $ (6.7) $ 396.9