Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenues from services	$ 5,022.1	$ 4,861.3	$ 9,609.8	$ 9,403.5
Cost of services	4,161.4	4,030.7	7,975.3	7,810.9
Gross profit	860.7	830.6	1,634.5	1,592.6
Selling and administrative expenses	664.7	651.9	1,306.8	1,291.1
Operating profit	196.0	178.7	327.7	301.5
Interest and other expenses	10.3	7.2	23.0	17.8
Earnings before income taxes	185.7	171.5	304.7	283.7
Provision for income taxes	70.3	65.8	117.6	112.3
Net earnings	$ 115.4	$ 105.7	$ 187.1	$ 171.4
Net earnings per share - basic (in dollars per share)	$ 1.61	$ 1.35	$ 2.59	$ 2.18
Net earnings per share - diluted (in dollars per share)	$ 1.60	$ 1.33	$ 2.57	$ 2.16
Weighted average shares - basic (in shares)	71.6	78.3	72.2	78.5
Weighted average shares - diluted (in shares)	72.3	79.3	72.9	79.5