TC PipeLines, LP (the Partnership), acquires, owns and participates in the management of energy infrastructure businesses in North America. The Company�s pipeline systems transport natural gas in the United States. The Partnership is managed by the Company�s General Partner, which is an indirect, wholly-owned subsidiary of TransCanada. The Company has equity ownership interests in four natural gas interstate pipeline systems. The Company�s pipeline systems include Great Lakes, Northern Border, GTN, Bison, North Baja and Tuscarora. In July 2013, TC PipeLines, LP announced the closing of its acquisition of an additional 45% interest in each of Gas Transmission Northwest LLC (GTN) and Bison Pipeline LLC (Bison) from subsidiaries of TransCanada Corporation.