CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenues from services	$ 20,863,500,000	$ 21,991,200,000	$ 21,034,300,000
Cost of services	17,488,400,000	18,412,200,000	17,549,700,000
Gross profit	3,375,100,000	3,579,000,000.0	3,484,600,000
Selling and administrative expenses, excluding goodwill impairment charge	2,666,200,000	2,782,300,000	2,695,400,000
Goodwill impairment charge	64,000,000.0
Selling and administrative expenses	2,730,200,000	2,782,300,000	2,695,400,000
Operating profit	644,900,000	796,700,000	789,200,000
Interest and other (income) expenses, net	(40,600,000)	42,000,000.0	51,900,000
Earnings before income taxes	685,500,000	754,700,000	737,300,000
Provision for income taxes	219,800,000	198,000,000.0	191,900,000
Net earnings	$ 465,700,000	$ 556,700,000	$ 545,400,000
Net earnings per share - basic (in dollars per share)	$ 7.78	$ 8.62	$ 8.13
Net earnings per share - diluted (in dollars per share)	$ 7.72	$ 8.56	$ 8.04
Weighted average shares - basic (in shares)	59.9	64.6	67.1
Weighted average shares - diluted (in shares)	60.3	65.1	67.9