RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 6		$ 6		$ 6
Amount included in receivables from related party	1		1		2
Great Lakes | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	12	$ 16
Impact on the Partnership's net income attributable to controlling interests	5	7
Northern Border | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	10	9
Impact on the Partnership's net income attributable to controlling interests	5	4
PNGTS | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	1	2
Impact on the Partnership's net income attributable to controlling interests	1	1
GTN | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	11	8
Impact on the Partnership's net income attributable to controlling interests	8	7
Bison | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged		1
Impact on the Partnership's net income attributable to controlling interests		1
North Baja | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	2	1
Impact on the Partnership's net income attributable to controlling interests	1	1
Tuscarora | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	1	1
Impact on the Partnership's net income attributable to controlling interests	1	1
General Partner | Reimbursement of costs of services provided
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged	1	$ 1	2	$ 2
TC Energy | Great Lakes
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	5		$ 5		3
Percentage of capital and operating costs charged			100.00%	100.00%
Amount included in receivables from related party	$ 13		$ 13		18
TC Energy | Great Lakes | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			23	$ 24
Impact on the Partnership's net income attributable to controlling interests			$ 10	$ 11
Percentage of capital and operating costs charged			100.00%	100.00%
TC Energy | Great Lakes | 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%	72.00%		70.00%
TC Energy | Northern Border
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 4		$ 4		3
Percentage of capital and operating costs charged			100.00%	100.00%
TC Energy | Northern Border | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			$ 19	$ 18
Impact on the Partnership's net income attributable to controlling interests			$ 9	$ 8
Percentage of capital and operating costs charged			100.00%	100.00%
TC Energy | PNGTS
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	1		$ 1		1
Percentage of capital and operating costs charged			100.00%	100.00%
TC Energy | PNGTS | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			$ 3	$ 4
Impact on the Partnership's net income attributable to controlling interests			$ 2	$ 2
Percentage of capital and operating costs charged			100.00%	100.00%
TC Energy | PNGTS | Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Amount included in receivables from related party	0		$ 0		0
Revenues from related party	0	$ 1	0
TC Energy | GTN
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	4		4		4
TC Energy | GTN | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			21	$ 16
Impact on the Partnership's net income attributable to controlling interests			16	14
TC Energy | Bison
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable					1
TC Energy | Bison | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			1	3
Impact on the Partnership's net income attributable to controlling interests			1	3
TC Energy | North Baja
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable	$ 1		1
TC Energy | North Baja | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			3	2
Impact on the Partnership's net income attributable to controlling interests			2	2
TC Energy | Tuscarora
Capital and operating costs charged to the pipeline systems and amount payable
Net amounts payable					$ 1
TC Energy | Tuscarora | Capital and operating costs
Capital and operating costs charged to the pipeline systems and amount payable
Costs charged			2	2
Impact on the Partnership's net income attributable to controlling interests			2	2
ANR Pipeline Company | Great Lakes | Transportation contracts
Capital and operating costs charged to the pipeline systems and amount payable
Contract term		15 years
Total contract value		$ 1,300		$ 1,300
Affiliates | PNGTS | Construction of facilities
Capital and operating costs charged to the pipeline systems and amount payable
Reimbursement of costs			$ 99