RELATED PARTY TRANSACTIONS - Summary of related party transactions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Accounts payable to affiliates	$ 32		$ 32		$ 8
Great Lakes | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	4		4		5
Great Lakes | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	35	$ 12	57	$ 35
Impact on the Partnership's net income attributable to controlling interests	4	4	$ 13	14
Percentage of capital and operating costs charged			100.00%
Northern Border | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	3		$ 3		4
Northern Border | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	9	10	29	29
Impact on the Partnership's net income attributable to controlling interests	4	4	$ 12	13
Percentage of capital and operating costs charged			100.00%
GTN | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	30		$ 30		5
GTN | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	33	11	57	32
Impact on the Partnership's net income attributable to controlling interests	7	9	22	25
Bison | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	0		0		0
Bison | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	0	1	1	2
Impact on the Partnership's net income attributable to controlling interests	0	0	1	1
North Baja | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	0		0		1
North Baja | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	4	1	6	4
Impact on the Partnership's net income attributable to controlling interests	1	1	3	3
Tuscarora | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	0		0		0
Tuscarora | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	3	1	5	3
Impact on the Partnership's net income attributable to controlling interests	0	1	2	3
PNGTS | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	1		1		$ 1
PNGTS | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	1	2	4	5
Impact on the Partnership's net income attributable to controlling interests	$ 0	$ 1	$ 2	$ 3
Percentage of capital and operating costs charged			100.00%