Acquisitions, Goodwill, and Other Intangible Assets (Schedule of Goodwill) (Details) - USD ($) $ in Millions			12 Months Ended
	Jun. 30, 2022	Jun. 01, 2022	Dec. 31, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Goodwill, Beginning Balance			$ 1,578.8	$ 1,571.7
Goodwill, Foreign Currency Translation Gain (Loss)			(12.9)	(7.1)
Goodwill, Ending Balance			1,562.0	1,578.8
Goodwill, Written off Related to Sale of Business Unit			(3.9)
Operating Segments
Goodwill [Roll Forward]
Goodwill, Beginning Balance			1,509.2	1,501.1
Goodwill, Foreign Currency Translation Gain (Loss)			(12.5)	(8.1)
Goodwill, Ending Balance			1,492.8	1,509.2
Goodwill, Written off Related to Sale of Business Unit			(3.9)
Morningstar Credit Segment [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance			108.6	106.9
Goodwill, Foreign Currency Translation Gain (Loss)			(3.4)	(1.7)
Goodwill, Ending Balance			105.2	108.6
Morningstar Credit Segment [Member] | Operating Segments
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit			0.0
PitchBook Segment [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance			607.4	607.4
Goodwill, Foreign Currency Translation Gain (Loss)			0.0	0.0
Goodwill, Ending Balance			607.4	607.4
PitchBook Segment [Member] | Operating Segments
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit			0.0
Morningstar Data and Analytics Segment [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance			605.5	600.3
Goodwill, Foreign Currency Translation Gain (Loss)			(7.6)	(5.2)
Goodwill, Ending Balance			594.0	605.5
Morningstar Data and Analytics Segment [Member] | Operating Segments
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit			(3.9)
Morningstar Retirement Segment [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance			93.5	93.5
Goodwill, Foreign Currency Translation Gain (Loss)			0.0	0.0
Goodwill, Ending Balance			93.5	93.5
Morningstar Retirement Segment [Member] | Operating Segments
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit			0.0
Corporate Segment and Other Operating Segment
Goodwill [Roll Forward]
Goodwill, Beginning Balance			69.6	70.6
Goodwill, Foreign Currency Translation Gain (Loss)			(0.4)	1.0
Goodwill, Ending Balance			69.2	69.6
Corporate Segment and Other Operating Segment | Operating Segments
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit			0.0
Morningstar Wealth Segment [Member]
Goodwill [Roll Forward]
Goodwill, Beginning Balance			94.2	93.0
Goodwill, Foreign Currency Translation Gain (Loss)			(1.5)	(1.2)
Goodwill, Ending Balance			92.7	$ 94.2
Morningstar Wealth Segment [Member] | Operating Segments
Goodwill [Roll Forward]
Goodwill, Written off Related to Sale of Business Unit			$ 0.0
LCD
Goodwill [Roll Forward]
Goodwill, Acquired During Period		$ 386.0
Praemium
Goodwill [Roll Forward]
Goodwill, Acquired During Period	$ 21.9