Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenues from services	$ 3,742.2	$ 5,373.1	$ 8,361.3	$ 10,418.0
Cost of services	3,165.5	4,502.7	7,060.6	8,742.8
Gross profit	576.7	870.4	1,300.7	1,675.2
Selling and administrative expenses, excluding goodwill impairment charges	559.9	675.6	1,246.2	1,374.9
Goodwill impairment charges	66.8	64.0	66.8	64.0
Selling and administrative expenses	626.7	739.6	1,313.0	1,438.9
Operating (loss) profit	(50.0)	130.8	(12.3)	236.3
Interest and other expenses (income), net	5.8	(70.2)	26.3	(58.3)
(Loss) earnings before income taxes	(55.8)	201.0	(38.6)	294.6
Provision for income taxes	8.6	73.7	24.1	113.8
Net (loss) earnings	$ (64.4)	$ 127.3	$ (62.7)	$ 180.8
Net (loss) earnings per share - basic (in dollars per share)	$ (1.11)	$ 2.12	$ (1.07)	$ 3.00
Net (loss) earnings per share - diluted (in dollars per share)	$ (1.11)	$ 2.11	$ (1.07)	$ 2.98
Weighted average shares - basic (in shares)	58.2	60.0	58.5	60.3
Weighted average shares - diluted (in shares)	58.2	60.4	58.5	60.7