| Cover | May 31, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Amendment Flag | false |
| Document Period End Date | May 31, 2023 |
| Entity File Number | 811-07626 |
| Entity Registrant Name | Putnam Municipal Opportunities Trust |
| Entity Central Index Key | 0000900422 |
| Entity Tax Identification Number | 04-3187549 |
| Entity Incorporation, State or Country Code | MA |
| Entity Address, Address Line One | 100 Federal Street |
| Entity Address, City or Town | Boston |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02110 |
| City Area Code | 617 |
| Local Phone Number | 292-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Shares of beneficial interest |
| Trading Symbol | PMO |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
