EARNINGS PER COMMON SHARE AND DIVIDENDS PER SHARE - Diluted (Details) - $ / shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Weighted average number of common shares outstanding diluted
Weighted average shares outstanding (in shares)	2,024.0	2,021.0	2,023.0	2,020.0
Effect of dilutive options (in shares)	2.0	0.0	2.0	1.0
Diluted weighted average shares outstanding (in shares)	2,026.0	2,021.0	2,025.0	2,021.0
Stock options
Weighted average number of common shares outstanding diluted
Antidilutive securities excluded from the diluted earnings per common share calculation (in shares)	13.3	34.1	20.5	28.5
Weighted average exercise price of antidilutive securities (in Canadian dollars per share)	$ 56.16	$ 50.55	$ 52.19	$ 51.85