Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenues from services	$ 5,088.2	$ 4,972.5	$ 14,698.0	$ 14,376.0
Cost of services	4,229.9	4,120.4	12,205.2	11,931.3
Gross profit	858.3	852.1	2,492.8	2,444.7
Selling and administrative expenses	647.2	645.8	1,954.0	1,936.9
Operating profit	211.1	206.3	538.8	507.8
Interest and other expenses	11.4	9.4	34.4	27.2
Earnings before income taxes	199.7	196.9	504.4	480.6
Provision for income taxes	70.5	73.0	188.1	185.3
Net earnings	$ 129.2	$ 123.9	$ 316.3	$ 295.3
Net earnings per share - basic (in dollars per share)	$ 1.89	$ 1.63	$ 4.46	$ 3.80
Net earnings per share - diluted (in dollars per share)	$ 1.87	$ 1.61	$ 4.42	$ 3.75
Weighted average shares - basic (in shares)	68.4	76.1	70.9	77.7
Weighted average shares - diluted (in shares)	69.0	77.0	71.6	78.7