CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenues from services	$ 18,001,000,000.0	$ 20,863,500,000	$ 21,991,200,000
Cost of services	15,176,300,000	17,488,400,000	18,412,200,000
Gross profit	2,824,700,000	3,375,100,000	3,579,000,000.0
Selling and administrative expenses, excluding goodwill impairment charges	2,570,300,000	2,666,200,000	2,782,300,000
Goodwill impairment charges	66,800,000	64,000,000.0
Selling and administrative expenses	2,637,100,000	2,730,200,000	2,782,300,000
Operating profit	187,600,000	644,900,000	796,700,000
Interest and other expenses (income), net	39,900,000	(40,600,000)	42,000,000.0
Earnings before income taxes	147,700,000	685,500,000	754,700,000
Provision for income taxes	123,900,000	219,800,000	198,000,000.0
Net earnings	$ 23,800,000	$ 465,700,000	$ 556,700,000
Net earnings per share - basic	$ 0.41	$ 7.78	$ 8.62
Net earnings per share - diluted	$ 0.41	$ 7.72	$ 8.56
Weighted average shares - basic	58.0	59.9	64.6
Weighted average shares - diluted	58.3	60.3	65.1