Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenues from services	$ 5,074.1	$ 5,277.1	$ 10,217.4	$ 10,201.5
Cost of services	4,152.9	4,417.0	8,399.1	8,573.3
Gross profit	921.2	860.1	1,818.3	1,628.2
Selling and administrative expenses	740.5	690.2	1,498.9	1,359.9
Operating profit	180.7	169.9	319.4	268.3
Interest and other expenses, net	6.7	2.8	9.4	8.2
Earnings before income taxes	174.0	167.1	310.0	260.1
Provision for income taxes	51.8	55.5	96.2	86.5
Net earnings	$ 122.2	$ 111.6	$ 213.8	$ 173.6
Net earnings (loss) per share - basic	$ 2.32	$ 2.05	$ 4.02	$ 3.17
Net earnings (loss) per share - diluted	$ 2.29	$ 2.02	$ 3.97	$ 3.13
Weighted average shares - basic (in shares)	52.7	54.5	53.2	54.8
Weighted average shares - diluted (in shares)	53.4	55.4	53.8	55.5