EARNINGS PER COMMON SHARE - SCHEDULE OF EARNINGS PER BASIC AND DILUTED BY COMMON CLASS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income attributable to American Tower Corporation common stockholders	$ 415.0	$ 397.4
Basic weighted average common shares outstanding (in shares)	443,055	441,351
Dilutive securities (in shares)	2,777	3,270
Diluted weighted average common shares outstanding (in shares)	445,832	444,621
Basic net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 0.94	$ 0.90
Diluted net income attributable to American Tower Corporation common stockholders per common share (in dollars per share)	$ 0.93	$ 0.89