CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 1,916.6	$ 1,264.7	$ 1,225.4
Other comprehensive (loss) income:
Changes in fair value of cash flow hedges, each net of tax expense of $0	(0.1)	(0.1)	(0.4)
Reclassification of unrealized losses (gains) on cash flow hedges to net income, each net of tax expense of $0	0.2	0.3	(0.1)
Adjustment to redeemable noncontrolling interest	0.0	78.8	0.0
Purchase of noncontrolling interest	0.0	0.5	0.0
Foreign currency translation adjustments, net of tax expense (benefit) of $0.5, ($2.6), and $1.0, respectively	(157.9)	(869.3)	144.4
Other comprehensive (loss) income	(157.8)	(789.8)	143.9
Comprehensive income	1,758.8	474.9	1,369.3
Comprehensive loss (income) attributable to noncontrolling interests	3.8	96.9	(109.4)
Allocation of accumulated other comprehensive income resulting from purchase of noncontrolling interest and redeemable noncontrolling interest	(55.5)	0.0	0.0
Comprehensive income attributable to American Tower Corporation stockholders	$ 1,707.1	$ 571.8	$ 1,259.9