RELATED PARTY TRANSACTIONS - Summary of related party transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Accounts payable to affiliates	$ 6		$ 6		$ 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	11	$ 12	22	$ 23
Impact on the Partnership's net income attributable to controlling interests	5	5	$ 9	10
Percentage of capital and operating costs charged			100.00%
Northern Border | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	4		$ 4		4
Northern Border | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	10	10	20	19
Impact on the Partnership's net income attributable to controlling interests	4	5	$ 8	9
Percentage of capital and operating costs charged			100.00%
GTN | TC Energy
Related Party Transaction [Line Items]
Accounts payable to affiliates	4		$ 4		5
GTN | TC Energy | Capital and operating costs
Related Party Transaction [Line Items]
Costs charged	12	11	24	21
Impact on the Partnership's net income attributable to controlling interests	7	8	15	16
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	1	0	1	1
Impact on the Partnership's net income attributable to controlling interests	1	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	1	2	2	3
Impact on the Partnership's net income attributable to controlling interests	1	1	2	2
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	1	1	2	2
Impact on the Partnership's net income attributable to controlling interests	1	1	2	2
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	1	3	3
Impact on the Partnership's net income attributable to controlling interests	$ 1	$ 1	$ 2	$ 2
Percentage of capital and operating costs charged			100.00%