Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenues from services	$ 5,174.8	$ 5,022.1	$ 9,932.0	$ 9,609.8
Cost of services	4,313.1	4,161.4	8,282.5	7,975.3
Gross profit	861.7	860.7	1,649.5	1,634.5
Selling and administrative expenses	667.1	664.7	1,327.9	1,306.8
Operating profit	194.6	196.0	321.6	327.7
Interest and other expenses	10.4	10.3	25.3	23.0
Earnings before income taxes	184.2	185.7	296.3	304.7
Provision for income taxes	67.2	70.3	104.9	117.6
Net earnings	$ 117.0	$ 115.4	$ 191.4	$ 187.1
Net earnings per share - basic (in dollars per share)	$ 1.74	$ 1.61	$ 2.83	$ 2.59
Net earnings per share - diluted (in dollars per share)	$ 1.72	$ 1.60	$ 2.80	$ 2.57
Weighted average shares - basic (in shares)	67.4	71.6	67.5	72.2
Weighted average shares - diluted (in shares)	68.0	72.3	68.3	72.9