REVENUES (Details) $ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2019 CAD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 CAD ($)
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		$ 5,756		$ 6,296
Revenues		12,856		12,726
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		17		718
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		5,739		5,578
Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		3,600		3,249
Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		134		166
Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		116		205
Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		1,856		1,926
Revenues		1,876		1,926
Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		50		57
Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer				693
Revenue not from contract with customers		6,632		6,575
Revenues		6,632		7,268
Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		468		(145)
Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		2,241		2,098
Liquids Pipelines | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Liquids Pipelines | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		2,241		2,098
Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		1,306		1,910
Gas Transmission and Midstream | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		693
Gas Transmission and Midstream | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		1,306		1,217
Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		2,159		2,231
Gas Distribution | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		17		25
Gas Distribution | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		2,142		2,206
Renewable Power Generation and Transmission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		50		57
Renewable Power Generation and Transmission | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Renewable Power Generation and Transmission | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		50		57
Energy Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Energy Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Energy Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		2,241		2,098
Revenues		2,658		1,909
Business segments | Liquids Pipelines | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		2,214		2,058
Business segments | Liquids Pipelines | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		27		40
Business segments | Liquids Pipelines | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Liquids Pipelines | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Liquids Pipelines | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Liquids Pipelines | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer				0
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		340		(269)
Business segments | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		1,306		1,910
Revenues		1,318		1,937
Business segments | Gas Transmission and Midstream | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		1,137		952
Business segments | Gas Transmission and Midstream | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		53		60
Business segments | Gas Transmission and Midstream | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		116		205
Business segments | Gas Transmission and Midstream | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Gas Transmission and Midstream | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Gas Transmission and Midstream | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer				693
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		10		25
Business segments | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		2,159		2,231
Revenues		2,191		2,237
Business segments | Gas Distribution | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		249		239
Business segments | Gas Distribution | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		54		66
Business segments | Gas Distribution | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Gas Distribution | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		1,856		1,926
Business segments | Gas Distribution | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Gas Distribution | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer				0
Revenue not from contract with customers		0		0
Business segments | Gas Distribution | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		29		2
Business segments | Renewable Power Generation and Transmission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		50		57
Revenues		152		157
Business segments | Renewable Power Generation and Transmission | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		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
Business segments | Renewable Power Generation and Transmission | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Renewable Power Generation and Transmission | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Renewable Power Generation and Transmission | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		50		57
Business segments | Renewable Power Generation and Transmission | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer				0
Revenue not from contract with customers		0		0
Business segments | Renewable Power Generation and Transmission | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		102		100
Business segments | Energy Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Revenues		6,673		6,632
Business segments | Energy Services | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Energy Services | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Energy Services | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Energy Services | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Energy Services | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer		0		0
Business segments | Energy Services | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer				0
Revenue not from contract with customers		6,632		6,575
Business segments | Energy Services | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		6		0
Eliminations and Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 0		$ 0
Revenues		(136)		(146)
Eliminations and Other | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0		0
Eliminations and Other | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0		0
Eliminations and Other | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0		0
Eliminations and Other | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0		0
Eliminations and Other | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 0		0
Eliminations and Other | Commodity
Disaggregation of Revenue [Line Items]
Revenue from contract with customer			$ 0
Revenue not from contract with customers		0		0
Eliminations and Other | Other Revenue
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		(19)		(3)
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		(117)		(143)
Revenues		(136)		(146)
Intersegment Eliminations | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		77		80
Intersegment Eliminations | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		2		2
Intersegment Eliminations | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		3		4
Intersegment Eliminations | Renewable Power Generation and Transmission
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		0		0
Intersegment Eliminations | Energy Services
Disaggregation of Revenue [Line Items]
Revenue not from contract with customers		$ 35		$ 57