STOCK OPTION AND STOCK UNIT PLANS - PSUs and RSUs (Details) - CAD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Performance Stock Units (PSUs)
Number
Units outstanding at beginning of year (in shares)	3,249
Units granted (in shares)	2,128
Units cancelled (in shares)	(214)
Units matured (in shares)	(2,218)
Dividend reinvestment (in shares)	235
Units outstanding at end of year (in shares)	3,180	3,249
Weighted Average Remaining Contractual Life (years)
Units outstanding at end of year	1 year 1 month 6 days
Aggregate Intrinsic Value
Units outstanding at end of year	$ 175
Stock units, additional disclosures
Total amount paid	$ 123	$ 90	$ 70
Restricted Stock Units (RSU)
Number
Units outstanding at beginning of year (in shares)	3,565
Units granted (in shares)	1,373
Units cancelled (in shares)	(246)
Units matured (in shares)	(1,401)
Dividend reinvestment (in shares)	280
Units outstanding at end of year (in shares)	3,571	3,565
Weighted Average Grant Date Fair Value
Units outstanding at beginning of year	$ 49.64
Units granted	52.05
Units cancelled	52.06
Units matured	51.05
Dividend reinvestment	50.88
Units outstanding at end of year	$ 50.69	$ 49.64
Weighted Average Remaining Contractual Life (years)
Units outstanding at end of year	10 months 24 days
Aggregate Intrinsic Value
Units outstanding at end of year	$ 177
Stock units, additional disclosures
Total amount paid	$ 56	$ 32	$ 72