| Cover | Apr. 28, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 28, 2021 |
| Entity File Number | 000-51280 |
| Entity Registrant Name | MORNINGSTAR, INC. |
| Entity Central Index Key | 0001289419 |
| Entity Tax Identification Number | 36-3297908 |
| Entity Incorporation, State or Country Code | IL |
| Entity Address, Address Line One | 22 West Washington Street |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60602 |
| City Area Code | 312 |
| Local Phone Number | 696-6000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, no par value |
| Trading Symbol | MORN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
