CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenues from services	$ 21,991.2	$ 21,034.3	$ 19,654.1
Cost of services	18,412.2	17,549.7	16,320.3
Gross profit	3,579.0	3,484.6	3,333.8
Selling and administrative expenses	2,782.3	2,695.4	2,588.3
Operating profit	796.7	789.2	745.5
Interest and other expenses	42.0	51.9	44.2
Earnings before income taxes	754.7	737.3	701.3
Provision for income taxes	198.0	191.9	257.6
Net earnings	$ 556.7	$ 545.4	$ 443.7
Net earnings per share - basic (in dollars per share)	$ 8.62	$ 8.13	$ 6.33
Net earnings per share - diluted (in dollars per share)	$ 8.56	$ 8.04	$ 6.27
Weighted average shares - basic (in shares)	64.6	67.1	70.1
Weighted average shares - diluted (in shares)	65.1	67.9	70.8