RELATED PARTY TRANSACTIONS (Details) MMBTU / d in Thousands		1 Months Ended	12 Months Ended
	Aug. 01, 2020 USD ($)	Sep. 21, 2017 Bcf	Dec. 31, 2020 USD ($) MMBTU / d	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			$ 7,000,000	$ 8,000,000
Amount included in receivables from related party			1,000,000	0
General Partner | Reimbursement of costs of services provided
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			4,000,000	4,000,000	$ 4,000,000
ANR Pipeline Company | Technology-Based Intangible Assets [Member]
Capital and operating costs charged to the pipeline systems and amount payable
Finite-lived intangible assets acquired	$ 51,000,000
TC Energy | ANR Pipeline Company | Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Contract term		10 years
Great Lakes | TransCanada's subsidiaries
Capital and operating costs charged to the pipeline systems and amount payable
Amount included in receivables from related party			17,000,000	19,000,000
Great Lakes | TC Energy
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			3,000,000	5,000,000
Great Lakes | TC Energy | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			66,000,000	47,000,000	44,000,000
Impact on the Partnership's net income attributable to controlling interests			16,000,000	20,000,000	19,000,000
Amount included in receivables from related party			27,000,000	34,000,000
Great Lakes | TC Energy | Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Revenues			$ 75,000,000	$ 76,000,000	$ 76,000,000
Great Lakes | TC Energy | Transportation contracts | Total net revenues | Customer concentration risk
Capital and operating costs charged to the pipeline systems and amount payable
Percent of total revenues			73.00%	73.00%	73.00%
Great Lakes | TC Energy | Affiliated rental revenue | Maximum
Capital and operating costs charged to the pipeline systems and amount payable
Percent of total revenues				1.00%	1.00%
Great Lakes | ANR Pipeline Company | Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Contract term			20 years		15 years
Transportation capacity per day | Bcf		0.711
Total contract value			$ 182,000,000		$ 1,300,000,000
Contract capacity | MMBTU / d			168
Contract value terminated						$ 1,100,000,000
Northern Border | TC Energy
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			$ 2,000,000	$ 4,000,000
Northern Border | TC Energy | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			39,000,000	39,000,000	36,000,000
Impact on the Partnership's net income attributable to controlling interests			16,000,000	18,000,000	16,000,000
Northern Border | Affiliates | Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Amount included in receivables from related party			0	0
Revenues from related party			800,000	0	0
PNGTS | TransCanada's subsidiaries | Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Amount included in receivables from related party			0	0
Revenues from related party				1,000,000	1,000,000
PNGTS | TC Energy
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			1,000,000	1,000,000
PNGTS | TC Energy | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			6,000,000	7,000,000	9,000,000
Impact on the Partnership's net income attributable to controlling interests			$ 3,000,000	4,000,000	5,000,000
PNGTS | Affiliates | Portland XPress expansion project (PXP), Phase III
Capital and operating costs charged to the pipeline systems and amount payable
Phase in period			3 years
GTN | TC Energy
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			$ 4,000,000	5,000,000
GTN | TC Energy | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			68,000,000	45,000,000	34,000,000
Impact on the Partnership's net income attributable to controlling interests			$ 29,000,000	$ 33,000,000	$ 28,000,000
Percentage of capital and operating costs charged			100.00%	100.00%	100.00%
Bison | TC Energy
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			$ 0	$ 0
Bison | TC Energy | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			2,000,000	2,000,000	$ 6,000,000
Impact on the Partnership's net income attributable to controlling interests			2,000,000	2,000,000	6,000,000
North Baja | TC Energy
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			0	1,000,000
North Baja | TC Energy | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			7,000,000	5,000,000	4,000,000
Impact on the Partnership's net income attributable to controlling interests			3,000,000	4,000,000	4,000,000
Tuscarora | TC Energy
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable			1,000,000	0
Tuscarora | TC Energy | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			6,000,000	4,000,000	4,000,000
Impact on the Partnership's net income attributable to controlling interests			$ 3,000,000	$ 4,000,000	$ 4,000,000
TC Pipelines, LP | ANR Pipeline Company | Technology-Based Intangible Assets [Member]
Capital and operating costs charged to the pipeline systems and amount payable
Finite-lived intangible assets acquired	$ 38,000,000