REVENUE - Disaggregation of Revenue (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 6,487	$ 5,391
Total revenues	15,097	12,137
Mark-to-market gains from hedging program	94	130
Revenues from lease contracts	164	159
Revenues from products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16	17
Revenue from products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,471	5,374
Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4,130	3,666
Storage and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	182	158
Gas gathering and processing revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15	7
Gas distribution revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,098	1,534
Total revenues	2,098	1,540
Electricity and transmission revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62	26
Commodity sales
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	8,325	6,429
Total revenues	8,325	6,429
Other revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	285	317
Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,736	2,355
Liquids Pipelines | Revenues from products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Liquids Pipelines | Revenue from products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,736	2,355
Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,293	1,202
Gas Transmission and Midstream | Revenues from products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Gas Transmission and Midstream | Revenue from products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,293	1,202
Gas Distribution and Storage
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,396	1,808
Gas Distribution and Storage | Revenues from products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	16	17
Gas Distribution and Storage | Revenue from products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,380	1,791
Renewable Power Generation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62	26
Renewable Power Generation | Revenues from products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Renewable Power Generation | Revenue from products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62	26
Business segments | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,736	2,355
Total revenues	3,055	2,699
Business segments | Liquids Pipelines | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,685	2,329
Business segments | Liquids Pipelines | Storage and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	51	26
Business segments | Liquids Pipelines | Gas gathering and processing revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Liquids Pipelines | Gas distribution revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Liquids Pipelines | Electricity and transmission revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Liquids Pipelines | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0
Business segments | Liquids Pipelines | Other revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	178	212
Business segments | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,293	1,202
Total revenues	1,300	1,214
Business segments | Gas Transmission and Midstream | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,194	1,121
Business segments | Gas Transmission and Midstream | Storage and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	84	74
Business segments | Gas Transmission and Midstream | Gas gathering and processing revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15	7
Business segments | Gas Transmission and Midstream | Gas distribution revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Gas Transmission and Midstream | Electricity and transmission revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Gas Transmission and Midstream | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0
Business segments | Gas Transmission and Midstream | Other revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	7	12
Business segments | Gas Distribution and Storage
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,396	1,808
Total revenues	2,411	1,823
Business segments | Gas Distribution and Storage | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	251	216
Business segments | Gas Distribution and Storage | Storage and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	58
Business segments | Gas Distribution and Storage | Gas gathering and processing revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Gas Distribution and Storage | Gas distribution revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,098	1,534
Business segments | Gas Distribution and Storage | Electricity and transmission revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Gas Distribution and Storage | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0
Business segments | Gas Distribution and Storage | Other revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	4	6
Business segments | Renewable Power Generation
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62	26
Total revenues	156	117
Business segments | Renewable Power Generation | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Renewable Power Generation | Storage and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Renewable Power Generation | Gas gathering and processing revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Renewable Power Generation | Gas distribution revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Renewable Power Generation | Electricity and transmission revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	62	26
Business segments | Renewable Power Generation | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0
Business segments | Renewable Power Generation | Other revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	94	91
Business segments | Energy Services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Total revenues	8,337	6,433
Business segments | Energy Services | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Energy Services | Storage and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Energy Services | Gas gathering and processing revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Energy Services | Gas distribution revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Energy Services | Electricity and transmission revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Business segments | Energy Services | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	8,325	6,429
Business segments | Energy Services | Other revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	2	0
Eliminations and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Total revenues	(162)	(149)
Eliminations and Other | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Eliminations and Other | Storage and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Eliminations and Other | Gas gathering and processing revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Eliminations and Other | Gas distribution revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Eliminations and Other | Electricity and transmission revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Eliminations and Other | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0
Eliminations and Other | Other revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	(4)
Intersegment revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	(162)	(145)
Total revenues	(162)	(149)
Intersegment revenue | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	141	132
Intersegment revenue | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0
Intersegment revenue | Gas Distribution and Storage
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	11	9
Intersegment revenue | Renewable Power Generation
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0
Intersegment revenue | Energy Services
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	$ 10	$ 4