Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Earnings Per Share, Basic [Abstract]
Consolidated net income	$ 78.5	$ 64.2
Weighted average common shares outstanding	42.8	42.7
Basic net income per share attributable to Morningstar, Inc.	$ 1.83	$ 1.50
Earnings Per Share, Diluted [Abstract]
Consolidated net income	$ 78.5	$ 64.2
Weighted average common shares outstanding	42.8	42.7
Net effect of dilutive stock options and restricted stock units	0.3	0.3
Weighted average common shares outstanding for computing diluted income per share	43.1	43.0
Diluted net income per share attributable to Morningstar, Inc.	$ 1.82	$ 1.49