SEGMENTED INFORMATION - Geographic Information and Property, Plant and Equipment (Details) - CAD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Geographic Information
Operating revenues (Note 4)	$ 11,298	$ 9,844	$ 10,432	$ 12,075	$ 13,424	$ 11,573	$ 13,215	$ 15,097	$ 43,649	$ 53,309	$ 47,071
Property, plant and equipment, net	104,641				104,460				104,641	104,460	100,067
Canada
Geographic Information
Operating revenues (Note 4)									23,781	27,498	20,474
Property, plant and equipment, net	48,570				47,602				48,570	47,602
US
Geographic Information
Operating revenues (Note 4)									19,868	25,811	$ 26,597
Property, plant and equipment, net	$ 56,071				$ 56,858				$ 56,071	$ 56,858