Revenues Revenue from External Customers by Geographic Areas (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 and other	44.4	154.1	158.8	274.8
Revenues	232.9	459.9	618.2	831.6
United States
Disaggregation of Revenue [Line Items]
Billboard	181.4	285.1	437.9	521.3
Revenues	225.0	435.3	593.9	790.0
Canada
Disaggregation of Revenue [Line Items]
Revenues	7.9	24.6	24.3	41.6
Transit and other
Disaggregation of Revenue [Line Items]
Transit and other	32.9	138.4	133.1	242.8
Transit and other | United States
Disaggregation of Revenue [Line Items]
Transit and other	32.1	134.5	130.3	236.7
Sports marketing and other
Disaggregation of Revenue [Line Items]
Transit and other	11.5	15.7	25.7	32.0
Sports marketing and other | United States
Disaggregation of Revenue [Line Items]
Transit and other	$ 11.5	$ 15.7	$ 25.7	$ 32.0