CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Revenues	$ 4,581.1	$ 4,009.5	$ 3,502.1
Cost of services	3,211.5	2,867.1	2,554.9
Gross profit	1,369.6	1,142.4	947.2
Selling, general and administrative expenses	895.0	735.8	615.0
Amortization of intangible assets	65.1	55.7	51.0
Operating income	409.5	350.9	281.2
Interest expense	(45.9)	(37.5)	(39.7)
Income before income taxes	363.6	313.4	241.5
Provision for income taxes	96.7	81.6	63.9
Income from continuing operations	266.9	231.8	177.6
Income from discontinued operations, net of income taxes	1.2	178.1	22.7
Net income	$ 268.1	$ 409.9	$ 200.3
Basic —
Continuing operations (in dollars per share)	$ 5.27	$ 4.40	$ 3.37
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0.03	3.38	0.43
Earnings per share (in dollars per share)	5.30	7.78	3.80
Diluted —
Continuing operations (in dollars per share)	5.21	4.33	3.33
Discontinued operations (in dollars per share)	0.02	3.33	0.43
Earnings per share (in dollars per share)	$ 5.23	$ 7.66	$ 3.76
Shares and share equivalents used to calculate earnings per share:
Basic (in shares)	50.6	52.7	52.7
Diluted (in shares)	51.3	53.5	53.3
Reconciliation of net income to comprehensive income:
Net income	$ 268.1	$ 409.9	$ 200.3
Foreign currency translation adjustment	(2.4)	0.7	6.0
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	$ 265.7	$ 410.6	$ 206.3