Supplementary Data Accrued Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Salaries, benefits and related expenses	$ 300.1	$ 441.7
Office and related expenses	51.9	53.2
Acquisition obligations	43.4	42.0
Interest	14.6	16.4
Other	118.1	121.4
Total accrued liabilities	$ 528.1	$ 674.7