Commitment and Contingencies MTA Agreement Schedule (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Change In MTA Deployment Costs [Roll Forward]
Prepaid MTA equipment deployment costs, beginning of period			$ 171.5	$ 79.5	$ 79.5
Intangible assets, gross, beginning of period			1,697.8
MTA deployment costs, beginning of period			209.8	94.3	94.3
Amortization of intangible assets	$ 21.7	$ 27.6	48.0	52.3
MTA equipment development cost additions			34.3		150.8
Prepaid MTA equipment deployment costs, end of period	199.8		199.8		171.5
Intangible assets, gross, end of period	1,734.6		1,734.6		1,697.8
MTA deployment costs, end of period	241.4		241.4		209.8
MTA equipment deployment costs
Change In MTA Deployment Costs [Roll Forward]
Deployment costs incurred			28.3		124.2
Recoupment			0.0		(32.2)
Amortization of intangible assets			(2.7)		(3.1)
Franchise agreements
Change In MTA Deployment Costs [Roll Forward]
Intangible assets, gross, beginning of period			497.4
Intangible assets, gross, end of period	503.6		503.6		497.4
Franchise agreements | MTA equipment deployment costs
Change In MTA Deployment Costs [Roll Forward]
Intangible assets, gross, beginning of period			38.3	$ 14.8	14.8
Intangible asset additions			6.0		26.6
Amortization of intangible assets			(2.7)		(3.1)
Intangible assets, gross, end of period	$ 41.6		$ 41.6		$ 38.3