| Cover | Dec. 14, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 14, 2020 |
| Entity File Number | 001-35358 |
| Entity Registrant Name | TC PipeLines, LP |
| Entity Central Index Key | 0001075607 |
| Entity Tax Identification Number | 52-2135448 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 700 Louisiana Street |
| Entity Address, Address Line Two | Suite 700 |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77002-2761 |
| City Area Code | 877 |
| Local Phone Number | 290-2772 |
| Written Communications | true |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Units representing limited partner interests |
| Trading Symbol | TCP |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
