Acquisitions, Goodwill and Other Intangible Assets (Schedule of Goodwill) (Details) - USD ($) $ in Millions		9 Months Ended
	Jun. 01, 2022	Sep. 30, 2025
Business Combination [Line Items]
Goodwill		$ 1,614.7
Goodwill [Roll Forward]
Goodwill, Beginning Balance		1,562.0
Foreign currency translation		20.6
Goodwill, Ending Balance		1,614.7
Operating Segments
Business Combination [Line Items]
Goodwill		1,544.7
Goodwill [Roll Forward]
Goodwill, Beginning Balance		1,492.8
Foreign currency translation		19.8
Goodwill, Ending Balance		1,544.7
Morningstar Data and Analytics Segment | Operating Segments
Business Combination [Line Items]
Goodwill		608.0
Goodwill [Roll Forward]
Goodwill, Beginning Balance		594.0
Foreign currency translation		14.0
Goodwill, Ending Balance		608.0
PitchBook Segment | Operating Segments
Business Combination [Line Items]
Goodwill		629.8
Goodwill [Roll Forward]
Goodwill, Beginning Balance		607.4
Foreign currency translation		0.0
Goodwill, Ending Balance		629.8
Morningstar Credit Segment | Operating Segments
Business Combination [Line Items]
Goodwill		119.1
Goodwill [Roll Forward]
Goodwill, Beginning Balance		105.2
Foreign currency translation		4.2
Goodwill, Ending Balance		119.1
Morningstar Wealth Segment | Operating Segments
Business Combination [Line Items]
Goodwill		94.3
Goodwill [Roll Forward]
Goodwill, Beginning Balance		92.7
Foreign currency translation		1.6
Goodwill, Ending Balance		94.3
Morningstar Retirement Segment | Operating Segments
Business Combination [Line Items]
Goodwill		93.5
Goodwill [Roll Forward]
Goodwill, Beginning Balance		93.5
Foreign currency translation		0.0
Goodwill, Ending Balance		93.5
Corporate and Other | Operating Segments
Business Combination [Line Items]
Goodwill		70.0
Goodwill [Roll Forward]
Goodwill, Beginning Balance		69.2
Foreign currency translation		0.8
Goodwill, Ending Balance		70.0
DealX
Business Combination [Line Items]
Goodwill, Acquired During Period		9.7
DealX | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		9.7
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		9.7
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		0.0
Lumonic
Business Combination [Line Items]
Goodwill, Acquired During Period	$ 22.4
Lumonic | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		22.4
Lumonic | Morningstar Data and Analytics Segment | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		0.0
Lumonic | PitchBook Segment | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		22.4
Lumonic | Morningstar Credit Segment | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		0.0
Lumonic | Morningstar Wealth Segment | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		0.0
Lumonic | Morningstar Retirement Segment | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		0.0
Lumonic | Corporate and Other | Operating Segments
Business Combination [Line Items]
Goodwill, Acquired During Period		$ 0.0