Segment Reporting (Revenue by Geographical Areas) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues from External Customers [Line Items]
Revenues	$ 972.3	$ 878.5	$ 1,896.0	$ 1,563.7
Revenue as Percentage of Consolidated Revenue	100.00%	100.00%	100.00%	100.00%
Domestic
Revenues from External Customers [Line Items]
Revenues	$ 929.8	$ 838.0	$ 1,810.9	$ 1,485.3
Revenue as Percentage of Consolidated Revenue	95.60%	95.40%	95.50%	95.00%
Foreign
Revenues from External Customers [Line Items]
Revenues	$ 42.5	$ 40.5	$ 85.1	$ 78.4
Revenue as Percentage of Consolidated Revenue	4.40%	4.60%	4.50%	5.00%