Supplemental Financial Information (Other Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Supplemental Financial Information [Abstract]
Unrecognized tax benefits (inclusive of interest and penalties)	$ 178.0	$ 142.9
Intangible Liabilities Noncurrent	59.6	0.0
Deferred revenue	51.2	120.9
Supplemental executive retirement plan liabilities	32.0	28.9
Deferred Tax Liabilities, Net, Noncurrent	18.5	5.2
Personnel costs	18.1	13.5
Deferred Rent Credit	17.1	9.4
Other Accrued Liabilities, Noncurrent	12.2	1.7
Other liabilities	$ 386.7	$ 322.5