CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 1,264.7	$ 1,225.4	$ 970.4
Other comprehensive (loss) income:
Changes in fair value of cash flow hedges, each net of tax expense of $0	(0.1)	(0.4)	(0.4)
Reclassification of unrealized losses on cash flow hedges to net income, each net of tax expense of $0	0.3	(0.1)	(0.3)
Reclassification of unrealized losses on cash flow hedges to net income, each net of tax expense of $0	78.8	0.0	0.0
Purchase of noncontrolling interest	0.5	0.0	0.0
Foreign currency translation adjustments, net of tax (benefit) expense of ($2.6), $1.0, and $3.8, respectively	(869.3)	144.4	(202.9)
Other comprehensive (loss) income	(789.8)	143.9	(203.6)
Comprehensive income	474.9	1,369.3	766.8
Comprehensive loss (income) attributable to non-controlling interest	96.9	(109.4)	18.2
Comprehensive income attributable to American Tower Corporation stockholders	$ 571.8	$ 1,259.9	$ 785.0