REVENUE (Details) $ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018 CAD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 CAD ($)
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 6,393
Revenues	12,726		$ 11,146
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	718
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	5,675
Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3,249
Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	166
Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	205
Gas Distribution Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,926
Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	154
Commodity sales
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	693
Revenues	6,575
Other Revenue
Disaggregation of Revenue [Line Items]
Revenues	(242)
Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,098
Liquids Pipelines | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Liquids Pipelines | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,098
Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,910
Gas Transmission and Midstream | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	693
Gas Transmission and Midstream | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,217
Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,231
Gas Distribution | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	25
Gas Distribution | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,206
Green Power and Transmission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	154
Green Power and Transmission | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Green Power and Transmission | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	154
Energy Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Energy Services | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Energy Services | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,098
Revenues	1,909		2,155
Business segments | Liquids Pipelines | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,058
Business segments | Liquids Pipelines | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	40
Business segments | Liquids Pipelines | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Liquids Pipelines | Gas Distribution Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Liquids Pipelines | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Liquids Pipelines | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Revenues	0
Business segments | Liquids Pipelines | Other Revenue
Disaggregation of Revenue [Line Items]
Revenues	(269)
Business segments | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,910
Revenues	1,937
Business segments | Gas Transmission and Midstream | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	952
Business segments | Gas Transmission and Midstream | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	60
Business segments | Gas Transmission and Midstream | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	205
Business segments | Gas Transmission and Midstream | Gas Distribution Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Gas Transmission and Midstream | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Gas Transmission and Midstream | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	693
Revenues	0
Business segments | Gas Transmission and Midstream | Other Revenue
Disaggregation of Revenue [Line Items]
Revenues	25
Business segments | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2,231
Revenues	2,237
Business segments | Gas Distribution | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	239
Business segments | Gas Distribution | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	66
Business segments | Gas Distribution | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Gas Distribution | Gas Distribution Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,926
Business segments | Gas Distribution | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Gas Distribution | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Revenues	0
Business segments | Gas Distribution | Other Revenue
Disaggregation of Revenue [Line Items]
Revenues	2
Business segments | Green Power and Transmission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	154
Revenues	157		137
Business segments | Green Power and Transmission | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Green Power and Transmission | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Green Power and Transmission | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Green Power and Transmission | Gas Distribution Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Green Power and Transmission | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	154
Business segments | Green Power and Transmission | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Revenues	0
Business segments | Green Power and Transmission | Other Revenue
Disaggregation of Revenue [Line Items]
Revenues	3
Business segments | Energy Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Revenues	6,632
Business segments | Energy Services | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Energy Services | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Energy Services | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Energy Services | Gas Distribution Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Energy Services | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Business segments | Energy Services | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Revenues	6,575
Business segments | Energy Services | Other Revenue
Disaggregation of Revenue [Line Items]
Revenues	0
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(143)	$ 0
Intersegment Eliminations | Liquids Pipelines
Disaggregation of Revenue [Line Items]
Revenues	80
Intersegment Eliminations | Gas Transmission and Midstream
Disaggregation of Revenue [Line Items]
Revenues	2
Intersegment Eliminations | Gas Distribution
Disaggregation of Revenue [Line Items]
Revenues	4
Intersegment Eliminations | Green Power and Transmission
Disaggregation of Revenue [Line Items]
Revenues	0
Intersegment Eliminations | Energy Services
Disaggregation of Revenue [Line Items]
Revenues	57
Consolidation, Eliminations
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Revenues	(146)		$ (98)
Consolidation, Eliminations | Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Consolidation, Eliminations | Storage and Other Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Consolidation, Eliminations | Gas Gathering and Processing Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Consolidation, Eliminations | Gas Distribution Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Consolidation, Eliminations | Electricity and Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Consolidation, Eliminations | Commodity sales
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0
Revenues	0
Consolidation, Eliminations | Other Revenue
Disaggregation of Revenue [Line Items]
Revenues	$ (3)