CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 1,225.4	$ 970.4	$ 672.0
Other comprehensive (loss) income:
Changes in fair value of cash flow hedges, net of tax expense of $0, $0 and $0.1, respectively	(0.4)	(0.4)	0.9
Reclassification of unrealized losses on cash flow hedges to net income, net of tax expense of $0, $0 and $0.1, respectively	(0.1)	(0.3)	2.4
Foreign currency translation adjustments, net of tax expense (benefit) of $1.0, $3.8 million, and $(24.9), respectively	144.4	(202.9)	(1,078.9)
Other comprehensive income (loss)	143.9	(203.6)	(1,075.6)
Comprehensive income (loss)	1,369.3	766.8	(403.6)
Comprehensive (income) loss attributable to noncontrolling interest	(109.4)	18.2	45.9
Comprehensive income (loss) attributable to American Tower Corporation stockholders	$ 1,259.9	$ 785.0	$ (357.7)