CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenues from services	$ 20,724,400,000	$ 18,001,000,000.0	$ 20,863,500,000
Cost of services	17,316,900,000	15,176,300,000	17,488,400,000
Gross profit	3,407,500,000	2,824,700,000	3,375,100,000
Selling and administrative expenses, excluding goodwill impairment charges	2,822,100,000	2,570,300,000	2,666,200,000
Goodwill impairment charges	0	66,800,000	64,000,000.0
Selling and administrative expenses	2,822,100,000	2,637,100,000	2,730,200,000
Operating profit	585,400,000	187,600,000	644,900,000
Interest and other expenses (income), net	17,300,000	39,900,000	(40,600,000)
Earnings before income taxes	568,100,000	147,700,000	685,500,000
Provision for income taxes	185,700,000	123,900,000	219,800,000
Net earnings	$ 382,400,000	$ 23,800,000	$ 465,700,000
Net earnings per share - basic	$ 7.01	$ 0.41	$ 7.78
Net earnings per share - diluted	$ 6.91	$ 0.41	$ 7.72
Weighted average shares - basic	54.5	58.0	59.9
Weighted average shares - diluted	55.4	58.3	60.3