Revenues Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Billboard	$ 188.5	$ 305.8	$ 459.4	$ 556.8
Transit	44.4	154.1	158.8	274.8
Revenues	232.9	459.9	618.2	831.6
Static displays
Disaggregation of Revenue [Line Items]
Billboard	149.5	229.1	350.6	423.4
Transit	22.9	97.1	88.0	176.1
Digital displays
Disaggregation of Revenue [Line Items]
Billboard	31.3	66.2	91.7	113.2
Transit	6.6	28.4	34.3	45.0
Other
Disaggregation of Revenue [Line Items]
Billboard	7.7	10.5	17.1	20.2
Transit	3.4	12.9	10.8	21.7
Transit
Disaggregation of Revenue [Line Items]
Transit	32.9	138.4	133.1	242.8
Sports marketing and other
Disaggregation of Revenue [Line Items]
Transit	$ 11.5	$ 15.7	$ 25.7	$ 32.0