Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Revenues from services	$ 4,800.9	$ 5,140.6	$ 15,018.3	$ 15,342.1
Cost of services	3,922.4	4,287.6	12,321.5	12,860.9
Gross profit	878.5	853.0	2,696.8	2,481.2
Selling and administrative expenses	717.0	702.5	2,215.9	2,062.4
Operating profit	161.5	150.5	480.9	418.8
Interest and other expenses, net	4.7	4.9	14.1	13.1
Earnings before income taxes	156.8	145.6	466.8	405.7
Provision for income taxes	45.5	47.9	141.7	134.4
Net earnings	$ 111.3	$ 97.7	$ 325.1	$ 271.3
Net earnings (loss) per share - basic	$ 2.15	$ 1.80	$ 6.18	$ 4.96
Net earnings (loss) per share - diluted	$ 2.13	$ 1.77	$ 6.10	$ 4.90
Weighted average shares - basic (in shares)	51.7	54.3	52.6	54.7
Weighted average shares - diluted (in shares)	52.3	55.2	53.3	55.4