Consolidated Statements of Financial Position - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets, Current [Abstract]
Cash and cash equivalents	$ 59.1	$ 52.7
Restricted cash	1.8	1.4
Receivables, less allowances of $12.1 in 2019 and $10.7 in 2018	290.0	264.9
Prepaid lease and franchise costs	8.6	69.3
Prepaid MTA equipment deployment costs	55.4	18.9
Other prepaid expenses	15.8	13.9
Other current assets	5.1	8.4
Total current assets	435.8	429.5
Assets, Noncurrent [Abstract]
Property and equipment, net	666.2	652.9
Goodwill	2,083.1	2,079.7
Intangible assets	550.9	537.2
Operating lease assets	1,457.0	0.0
Prepaid MTA equipment deployment costs	116.1	60.6
Other assets	73.2	68.8
Total assets	5,382.3	3,828.7
Liabilities, Current [Abstract]
Accounts payable	67.9	56.5
Accrued compensation	56.1	47.1
Accrued interest	26.4	19.1
Accrued lease and franchise costs	55.3	44.2
Other accrued expenses	34.2	31.2
Deferred revenues	29.0	29.8
Short-term debt	195.0	160.0
Short-term operating lease liabilities	168.3	0.0
Other current liabilities	17.8	14.7
Total current liabilities	650.0	402.6
Liabilities, Noncurrent [Abstract]
Long-term debt, net	2,222.1	2,149.6
Deferred income tax liabilities, net	18.0	17.0
Asset retirement obligation	35.1	34.2
Operating lease liabilities	1,285.1	0.0
Other liabilities	45.6	80.0
Total liabilities	4,255.9	2,683.4
Commitments and contingencies
Equity [Abstract]
Common stock (2019 - 450.0 shares authorized, and 143.6 shares issued and outstanding; 2018 - 450.0 shares authorized, and 140.2 shares authorized, issued or outstanding)	1.4	1.4
Additional paid-in capital	2,074.7	1,995.0
Distribution in excess of earnings	(964.6)	(871.6)
Accumulated other comprehensive loss	(17.7)	(22.0)
Total stockholders’ equity	1,093.8	1,102.8
Non-controlling interests	32.6	42.5
Total equity	1,126.4	1,145.3
Total liabilities and equity	$ 5,382.3	$ 3,828.7