Condensed Consolidated Statements of Operations - 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]
Revenue	$ 1,743.6	$ 2,121.7	$ 3,639.0	$ 4,024.7
Costs and expenses:
Cost of services (exclusive of depreciation and amortization)	1,453.9	1,687.1	3,052.7	3,251.9
Operating, administrative and other	272.1	306.9	556.1	593.7
Depreciation and amortization	74.6	74.3	146.6	147.8
Restructuring, impairment and related charges	5.8	0.2	31.9	4.1
Total costs and expenses	1,806.4	2,068.5	3,787.3	3,997.5
Operating income (loss)	(62.8)	53.2	(148.3)	27.2
Interest expense, net of interest income	(38.8)	(38.2)	(75.3)	(75.4)
Earnings from equity method investments	1.7	0.5	3.0	1.3
Other income (expense), net	(8.6)	2.2	30.5	2.8
Earnings (loss) before income taxes	(108.5)	17.7	(190.1)	(44.1)
Provision (benefit) from income taxes	(7.7)	11.4	(34.2)	(29.5)
Net income (loss)	$ (100.8)	$ 6.3	$ (155.9)	$ (14.6)
Basic earnings (loss) per share:
Earnings (loss) per share attributable to common shareholders, basic (in dollars per share)	$ (0.46)	$ 0.03	$ (0.71)	$ (0.07)
Weighted average shares outstanding for basic earnings (loss) per share	220.4	216.9	220.2	216.8
Diluted earnings (loss) per share:
Earnings (loss) per share attributable to common shareholders, diluted (in dollars per share)	$ (0.46)	$ 0.03	$ (0.71)	$ (0.07)
Weighted average shares outstanding for diluted earnings (loss) per share	220.4	224.8	220.2	216.8