Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues from services	$ 5,248.9	$ 5,418.7	$ 15,666.9	$ 16,598.0
Cost of services	4,408.6	4,528.1	13,151.4	13,899.3
Gross profit	840.3	890.6	2,515.5	2,698.7
Selling and administrative expenses, excluding goodwill impairment charge	623.3	673.9	1,998.2	2,119.9
Goodwill impairment charge	0.0		64.0
Selling and administrative expenses	623.3	673.9	2,062.2	2,119.9
Operating profit	217.0	216.7	453.3	578.8
Interest and other expenses (income), net	12.2	11.8	(46.1)	38.4
Earnings before income taxes	204.8	204.9	499.4	540.4
Provision for income taxes	58.7	46.9	172.5	142.0
Net earnings	$ 146.1	$ 158.0	$ 326.9	$ 398.4
Net earnings per share - basic (in dollars per share)	$ 2.44	$ 2.45	$ 5.43	$ 6.08
Net earnings per share - diluted (in dollars per share)	$ 2.42	$ 2.43	$ 5.40	$ 6.03
Weighted average shares - basic (in shares)	59.9	64.5	60.2	65.6
Weighted average shares - diluted (in shares)	60.3	65.0	60.6	66.1