Document and Entity Information	3 Months Ended
	Mar. 31, 2012	Apr. 30, 2012
Document and Entity Information
Entity Registrant Name	TC PIPELINES LP
Entity Central Index Key	0001075607
Document Type	10-Q
Document Period End Date	Mar. 31, 2012
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		53,472,766
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1