CAPITAL STOCK - Summary of Stock Options Activities (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning of year, Shares (in shares)	4,298,000	4,872,000	4,593,000
Granted, Shares (in shares)	0	0	812,000
Exercised, Shares (in shares)	0	0	(29,000)
Forfeited, Shares (in shares)	(37,000)	(80,000)	(121,000)
Expired, Shares (in shares)	(724,000)	(494,000)	(383,000)
Outstanding, end of year, Shares (in shares)	3,537,000	4,298,000	4,872,000
Expected to vest, Shares (in shares)	150,000	495,000	1,274,000
Exercisable, end of year, Shares (in shares)	3,387,000	3,803,000	3,598,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding, beginning of year, weighted average exercise price (in USD per share)	$ 75.24	$ 75.95	$ 83.36
Granted, weighted average exercise price (in USD per share)	0	0	45.93
Exercised, weighted average exercise price (in USD per share)	0	0	41.79
Forfeited, weighted average exercise price (in USD per share)	44.98	34.58	74.58
Expired, weighted average exercise price (in USD per share)	92.14	88.82	104.21
Outstanding, end of year, weighted average exercise price (in USD per share)	72.10	75.24	75.95
Expected to vest, weighted average exercise price (in USD per share)	45.77	49.11	48.74
Exercisable, end of year, weighted average exercise price (in USD per share)	$ 73.26	$ 78.64	$ 85.59
Weighted average remaining contractual life for options outstanding	3 years 7 months 6 days
Aggregate intrinsic value for options outstanding	$ 0.0
Weighted average remaining contractual life for expected to vest	7 years
Aggregate intrinsic value for expected to vest	$ 0.0
Weighted average remaining contractual life for exercisable	3 years 4 months 24 days
Aggregate intrinsic value for exercisable	$ 0.0