RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Schedule of Unrealized Gains and Losses Associated With Changes in The Fair Value of Non-Qualifying Derivatives (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives			$ (308)	$ 997
Non- Qualifying Derivative Instruments
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives	$ 91	$ (270)	(351)	1,046
Foreign exchange contracts \| Non- Qualifying Derivative Instruments
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives	121	(467)	(512)	766
Interest rate contracts \| Non- Qualifying Derivative Instruments
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives	246	(8)	308	(48)
Commodity contracts \| Non- Qualifying Derivative Instruments
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives	(276)	205	(147)	331
Changes in regulatory assets/(liabilities)			(43)	49
Commodity contracts \| Non- Qualifying Derivative Instruments \| Location, Statement of Income, Balance [Axis]: us-gaap:Revenues \| Transportation revenue
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives			(28)	101
Commodity contracts \| Non- Qualifying Derivative Instruments \| Location, Statement of Income, Balance [Axis]: us-gaap:Revenues \| Commodity sales
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives			263	(46)
Commodity contracts \| Non- Qualifying Derivative Instruments \| Location, Statement of Income, Balance [Axis]: us-gaap:Revenues \| Commodity costs
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives			(331)	206
Commodity contracts \| Non- Qualifying Derivative Instruments \| Location, Statement of Income, Balance [Axis]: us-gaap:Revenues \| Operating and administrative expense
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives			(8)	21
Other contracts \| Non- Qualifying Derivative Instruments
The Effect of Derivative Instruments on the Statements of Earnings and Comprehensive Income
Unrealized gain (loss) on derivatives	$ 0	$ 0	$ 0	$ (3)