TC PipeLines, LP is a master limited partnership. The Company 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. As of December 31, 2016, the Company had four pipelines and equity ownership interests in three natural gas interstate pipeline systems that are collectively designed to transport approximately 9.1 billion cubic feet per day of natural gas from producing regions and import facilities to market hubs and consuming markets primarily in the Western, Midwestern and Eastern United States. The Company's pipeline systems include Gas Transmission Northwest LLC (GTN), Bison Pipeline LLC (Bison), North Baja Pipeline, LLC (North Baja), Tuscarora Gas Transmission Company (Tuscarora), Northern Border Pipeline Company (Northern Border), Portland Natural Gas Transmission System (PNGTS), and Great Lakes Gas Transmission Limited Partnership (Great Lakes).