SUPPLEMENTAL CASH FLOW INFORMATION - (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental cash flow information:
Cash paid for interest	$ 762.3	$ 750.2	$ 789.7
Tax refunds	27.0	11.2	25.0
Cash paid for income taxes (net of refunds of $27.0, $11.2 and $25.0, respectively)	146.3	147.5	163.9
Non-cash investing and financing activities:
Increase (decrease) in accounts payable and accrued expenses for purchases of property and equipment and construction activities	45.8	(21.0)	8.3
Purchases of property and equipment under finance leases, perpetual easements and capital leases	75.0	81.3	57.8
Fair value of debt assumed through acquisitions (1)	800.0	329.8	0.0
Acquisition of commercialization rights	0.0	0.0	24.8
Debt financed acquisition of communication sites	0.0	0.0	54.2
Settlement of third-party debt	$ (5.0)	$ 0.0	$ 0.0