Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue	$ 8,751.0	$ 8,219.9	$ 6,923.9
Costs and expenses:
Cost of services (exclusive of depreciation and amortization)	6,981.7	6,642.4	5,639.8
Operating, administrative and other	1,273.4	1,271.1	1,156.1
Depreciation and amortization	296.7	290.0	270.6
Restructuring, impairment and related charges	11.9	3.8	28.5
Total costs and expenses	8,563.7	8,207.3	7,095.0
Operating earnings (loss)	187.3	12.6	(171.1)
Interest expense, net of interest income	(150.6)	(228.8)	(183.1)
Earnings from equity method investments	2.6	1.9	1.4
Other income, net	3.5	3.5	11.0
Earnings (loss) before income taxes	42.8	(210.8)	(341.8)
Provision (benefit) from income taxes	42.6	(25.0)	(120.5)
Net income (loss)	$ 0.2	$ (185.8)	$ (221.3)
Basic earnings (loss) per share:
Earnings (loss) per share attributable to common shareholders, basic (in dollar per share)	$ 0.00	$ (1.09)	$ (1.54)
Weighted average shares outstanding for basic earnings (loss) per share (in shares)	217.7	171.2	143.9
Diluted earnings (loss) per share:
Earnings (loss) per share attributable to common shareholders, diluted (in dollars per share)	$ 0.00	$ (1.09)	$ (1.54)
Weighted average shares outstanding for diluted earnings (loss) per share (in shares)	224.5	171.2	143.9