CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenues	$ 4,009.5	$ 3,502.1	$ 3,415.6
Cost of services	2,867.1	2,554.9	2,444.1
Gross profit	1,142.4	947.2	971.5
Selling, general and administrative expenses	735.8	615.0	645.0
Amortization of intangible assets	55.7	51.0	50.3
Operating income	350.9	281.2	276.2
Interest expense	(37.5)	(39.7)	(52.9)
Write-off of loan costs	0.0	0.0	(18.9)
Income before income taxes	313.4	241.5	204.4
Provision for income taxes	81.6	63.9	54.7
Income from continuing operations	231.8	177.6	149.7
Income from discontinued operations, net of income taxes	178.1	22.7	25.0
Net income	$ 409.9	$ 200.3	$ 174.7
Basic —
Continuing operations (in dollars per share)	$ 4.40	$ 3.37	$ 2.84
Discontinued operations (in dollars per share)	3.38	0.43	0.47
Earnings per share (in dollars per share)	7.78	3.80	3.31
Diluted —
Continuing operations (in dollars per share)	4.33	3.33	2.80
Discontinued operations (in dollars per share)	3.33	0.43	0.48
Earnings per share (in dollars per share)	$ 7.66	$ 3.76	$ 3.28
Shares and share equivalents used to calculate earnings per share:
Basic (in shares)	52.7	52.7	52.8
Diluted (in shares)	53.5	53.3	53.4
Reconciliation of net income to comprehensive income:
Net income	$ 409.9	$ 200.3	$ 174.7
Foreign currency translation adjustment	0.7	6.0	(0.7)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent, Total	$ 410.6	$ 206.3	$ 174.0