CONSOLIDATED STATEMENTS OF COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 418.6	$ 407.6
Other comprehensive (loss) income:
Changes in fair value of cash flow hedges, each net of tax expense of $0	(0.0)	(0.1)
Reclassification of unrealized losses on cash flow hedges to net income, each net of tax expense of $0	0.0	0.1
Foreign currency translation adjustments, net of tax (benefit) expense of ($0.0) and $1.0, respectively	(1,343.5)	12.9
Other comprehensive (loss) income	(1,343.5)	12.9
Comprehensive (loss) income	(924.9)	420.5
Allocation of accumulated other comprehensive income resulting from purchase of noncontrolling interest and redeemable noncontrolling interest	(142.2)	(52.4)
Comprehensive loss attributable to noncontrolling interests	34.0	0.0
Comprehensive (loss) income attributable to American Tower Corporation stockholders	$ (1,033.1)	$ 368.1