Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue	$ 2,076.0	$ 1,709.3	$ 5,818.0	$ 4,871.2
Costs and expenses:
Cost of services (exclusive of depreciation and amortization)	1,687.2	1,421.3	4,725.2	4,037.6
Operating, administrative and other	307.4	276.0	914.2	838.8
Depreciation and amortization	71.6	64.1	213.0	193.0
Restructuring, impairment and related charges	(1.2)	2.5	2.8	12.7
Total costs and expenses	2,065.0	1,763.9	5,855.2	5,082.1
Operating income (loss)	11.0	(54.6)	(37.2)	(210.9)
Interest expense, net of interest income	(92.7)	(49.2)	(189.1)	(134.9)
Earnings from equity method investments	0.4	0.5	1.2	1.0
Other (expense) income, net	(0.3)	0.9	2.7	1.2
Loss before income taxes	(81.6)	(102.4)	(222.4)	(343.6)
Benefit from income taxes	(32.9)	(23.8)	(49.5)	(98.0)
Net loss	$ (48.7)	$ (78.6)	$ (172.9)	$ (245.6)
Basic and diluted loss per share:
Loss per share attributable to common shareholders (in dollars per share)	$ (0.26)	$ (0.55)	$ (1.09)	$ (1.71)
Weighted average shares outstanding for basic and diluted loss per share (in shares)	184.0	144.1	158.5	143.6