INCOME TAXES - Unrecognized Tax Benefits (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
UNRECOGNIZED TAX BENEFITS
Unrecognized tax benefits at beginning of year	$ 55	$ 76
Gross decreases for tax positions of prior year	(2)	(17)
Change in translation of foreign currency	(1)	1
Lapses of statute of limitations	(7)	(5)
Unrecognized tax benefits at end of year	$ 45	$ 55