REVENUES (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 4,552	$ 5,112	$ 10,308	$ 11,408
Revenues	13,263	10,745	26,119	23,471
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	20	659	37	1,377
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	4,532	4,453	10,271	10,031
Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3,514	3,188	7,114	6,437
Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	123	145	257	311
Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	115	231	231	436
Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	754	856	2,610	2,782
Revenues	755	856	2,631	2,782
Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	43	53	93	110
Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3	639	3	1,332
Revenue not from contract with customers	8,413	5,812	15,045	12,387
Revenues	8,416	6,451	15,048	13,719
Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	298	(179)	766	(324)
Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,255	2,121	4,496	4,219
Liquids Pipelines | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Liquids Pipelines | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,255	2,121	4,496	4,219
Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,277	1,879	2,583	3,789
Gas Transmission and Midstream | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3	639	3	1,332
Gas Transmission and Midstream | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,274	1,240	2,580	2,457
Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	977	1,059	3,136	3,290
Gas Distribution | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	17	20	34	45
Gas Distribution | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	960	1,039	3,102	3,245
Renewable Power Generation and Transmission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	43	53	93	110
Renewable Power Generation and Transmission | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Renewable Power Generation and Transmission | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	43	53	93	110
Energy Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Energy Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Energy Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,255	2,121	4,496	4,219
Revenues	2,569	1,950	5,227	3,859
Business segments | Liquids Pipelines | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,230	2,079	4,444	4,137
Business segments | Liquids Pipelines | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	25	42	52	82
Business segments | Liquids Pipelines | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Liquids Pipelines | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Liquids Pipelines | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Liquids Pipelines | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Revenue not from contract with customers	0	0	0	0
Business segments | Liquids Pipelines | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	199	(261)	539	(530)
Business segments | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,277	1,879	2,583	3,789
Revenues	1,288	1,864	2,606	3,801
Business segments | Gas Transmission and Midstream | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,113	958	2,250	1,910
Business segments | Gas Transmission and Midstream | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	46	51	99	111
Business segments | Gas Transmission and Midstream | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	115	231	231	436
Business segments | Gas Transmission and Midstream | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Gas Transmission and Midstream | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Gas Transmission and Midstream | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3	639	3	1,332
Revenue not from contract with customers	0	0	0	0
Business segments | Gas Transmission and Midstream | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	10	(17)	20	8
Business segments | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	977	1,059	3,136	3,290
Revenues	977	1,070	3,168	3,307
Business segments | Gas Distribution | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	171	151	420	390
Business segments | Gas Distribution | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	52	52	106	118
Business segments | Gas Distribution | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Gas Distribution | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	754	856	2,610	2,782
Business segments | Gas Distribution | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Gas Distribution | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Revenue not from contract with customers	0	0	0	0
Business segments | Gas Distribution | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	(3)	9	26	11
Business segments | Renewable Power Generation and Transmission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	43	53	93	110
Revenues	137	149	289	306
Business segments | Renewable Power Generation and Transmission | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Renewable Power Generation and Transmission | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Renewable Power Generation and Transmission | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Renewable Power Generation and Transmission | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Renewable Power Generation and Transmission | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	43	53	93	110
Business segments | Renewable Power Generation and Transmission | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Revenue not from contract with customers	0	0	0	0
Business segments | Renewable Power Generation and Transmission | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	94	96	196	196
Business segments | Energy Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Revenues	8,418	5,836	15,091	12,468
Business segments | Energy Services | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Energy Services | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Energy Services | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Energy Services | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Energy Services | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Business segments | Energy Services | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Revenue not from contract with customers	8,413	5,812	15,045	12,387
Business segments | Energy Services | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	(7)	0	(1)	0
Eliminations and Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Revenues	(126)	(124)	(262)	(270)
Eliminations and Other | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Eliminations and Other | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Eliminations and Other | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Eliminations and Other | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Eliminations and Other | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Eliminations and Other | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0	0	0
Revenue not from contract with customers	0	0	0	0
Eliminations and Other | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	5	(6)	(14)	(9)
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	(131)	(118)	(248)	(261)
Revenues	(126)	(124)	(262)	(270)
Intersegment Eliminations | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	115	90	192	170
Intersegment Eliminations | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	1	2	3	4
Intersegment Eliminations | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	3	2	6	6
Intersegment Eliminations | Renewable Power Generation and Transmission
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	0	0	0	0
Intersegment Eliminations | Energy Services
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers	$ 12	$ 24	$ 47	$ 81