ACQUISITIONS AND DISPOSITIONS - Summary of Estimated Fair Values Assigned to Net Assets (Details) $ / shares in Units, shares in Millions, CAD in Millions, $ in Millions		3 Months Ended	12 Months Ended
	Feb. 27, 2017 CAD shares	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CAD	Dec. 31, 2016 CAD	Dec. 31, 2015 CAD	Feb. 27, 2017 $ / shares
Fair value of net assets acquired:
Goodwill (Note 15)			CAD 34,457	CAD 78
Purchase price:
Cash			0	644	CAD 106
Fair value adjustment to long-term debt related to rate-regulated entities			1,114	0
Decrease to deferred amounts and other assets			CAD (138)	CAD (183)	CAD 364
Spectra Energy
Fair value of net assets acquired:
Current assets	CAD 2,432
Property, plant and equipment, net	33,555
Restricted long-term investments	144
Long-term investments	5,000
Deferred amounts and other assets	2,390
Intangible assets, net	1,288
Current liabilities (a)	(3,982)
Long-term debt	(21,444)
Other long-term liabilities	(1,983)
Deferred income taxes	(7,670)
Noncontrolling interests	(8,877)
Fair value of net assets acquired	853
Goodwill (Note 15)	36,656
Fair value of net assets acquired and goodwill	37,509
Purchase price:
Cash	3
Purchase price	37,509
Net carrying value of accounts receivable	1,174
Gross amount due	1,190
Not expected to be collected	16
Business Combination, adjustment, current assets | $		$ 67
Business Combination, adjustment, current liabilities | $		548
Business Combination, adjustment, long-term debt | $		$ 481
Reclassification from intangible assets to property, plant and equipment	830
Increase in the book value of debt	1,500
Fair value adjustment to long-term debt related to rate-regulated entities	629
Spectra Energy | Common shares
Purchase price:
Equity issued	37,429
Spectra Energy | Earned stock compensation awards
Purchase price:
Equity issued	CAD 77
Spectra Energy | SEP
Purchase price:
SEP common units outstanding to the public (in shares) | shares	78.4
Closing price per common unit (in USD per share) | $ / shares						$ 44.88
Spectra Energy | Various equity investments of acquiree
Purchase price:
Long-term investments (as a percent)	50.00%
Spectra Energy | PennEast
Purchase price:
Long-term investments (as a percent)	20.00%
Sabal Trail
Purchase price:
Increase to noncontrolling interests	CAD 85
BC Pipelines & Field Services
Purchase price:
Decrease to property, plant and equipment	1,955
Decrease to deferred income tax liabilities	661
Decrease to deferred amounts and other assets	530
Increase to noncontrolling interests	CAD 1,824