v3.26.3
Acquisitions, Goodwill and Other Intangible Assets (Schedule of Goodwill) (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Business Combination [Line Items]    
Goodwill $ 1,745.7  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 1,610.8  
Foreign currency translation and other (5.1)  
Goodwill, Ending Balance 1,745.7  
Operating Segments    
Business Combination [Line Items]    
Goodwill 1,535.8  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 1,540.7  
Foreign currency translation and other (4.9)  
Goodwill, Ending Balance 1,535.8  
Morningstar Data and Analytics Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill 604.0  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 608.6  
Foreign currency translation and other (4.6)  
Goodwill, Ending Balance 604.0  
PitchBook Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill 628.7  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 628.7  
Foreign currency translation and other 0.0  
Goodwill, Ending Balance 628.7  
Morningstar Credit Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill 117.9  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 119.6  
Foreign currency translation and other (1.7)  
Goodwill, Ending Balance 117.9  
Morningstar Wealth Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill 91.7  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 90.3  
Foreign currency translation and other 1.4  
Goodwill, Ending Balance 91.7  
Morningstar Retirement Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill 93.5  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 93.5  
Foreign currency translation and other 0.0  
Goodwill, Ending Balance 93.5  
Corporate and Other | Operating Segments    
Business Combination [Line Items]    
Goodwill 209.9  
Goodwill [Roll Forward]    
Goodwill, Beginning Balance 70.1  
Foreign currency translation and other (0.2)  
Goodwill, Ending Balance 209.9  
DealX    
Business Combination [Line Items]    
Goodwill, Acquired During Period 140.0 $ 9.7
DealX | Operating Segments    
Business Combination [Line Items]    
Goodwill, Acquired During Period 0.0  
DealX | Morningstar Data and Analytics Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill, Acquired During Period 0.0  
DealX | PitchBook Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill, Acquired During Period 0.0  
DealX | Morningstar Credit Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill, Acquired During Period 0.0  
DealX | Morningstar Wealth Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill, Acquired During Period 0.0  
DealX | Morningstar Retirement Segment | Operating Segments    
Business Combination [Line Items]    
Goodwill, Acquired During Period 0.0  
DealX | Corporate and Other | Operating Segments    
Business Combination [Line Items]    
Goodwill, Acquired During Period $ 140.0  
Lumonic    
Business Combination [Line Items]    
Goodwill, Acquired During Period   $ 21.3