Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenues from services	$ 5,522.4	$ 4,757.2
Cost of services	4,637.0	3,969.4
Gross profit	885.4	787.8
Selling and administrative expenses	731.6	659.9
Operating profit	153.8	127.9
Interest and other expenses	16.1	15.8
Earnings before income taxes	137.7	112.1
Provision for income taxes	40.7	37.7
Net earnings	$ 97.0	$ 74.4
Net earnings per share - basic (in dollars per share)	$ 1.46	$ 1.10
Net earnings per share - diluted (in dollars per share)	$ 1.45	$ 1.09
Weighted average shares - basic (in shares)	66.3	67.7
Weighted average shares - diluted (in shares)	66.9	68.4