Dispositions of Subsidiaries and Repositioning Actions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Severance	$ 68.4
Office lease consolidation and termination	73.5
Asset write-offs related to disposals and other costs	7.5
Repositioning Actions	149.4
Net Gain on Disposition of Subsidiaries	(178.4)	$ 0.0	$ 0.0
Salary and service costs
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	73.7
Net Gain on Disposition of Subsidiaries	0.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries	73.7
Occupancy and other costs
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	73.5
Net Gain on Disposition of Subsidiaries	0.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries	73.5
Net gain on disposition of subsidiaries
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	0.0
Net Gain on Disposition of Subsidiaries	(178.4)
Repositioning Actions and Net Gain on Disposition of Subsidiaries	178.4
Cost of services
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	147.2
Net Gain on Disposition of Subsidiaries	(178.4)
Repositioning Actions and Net Gain on Disposition of Subsidiaries	(31.2)
Selling, general and administrative expenses
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	2.2
Net Gain on Disposition of Subsidiaries	0.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries	2.2
Depreciation and amortization
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	0.0
Net Gain on Disposition of Subsidiaries	0.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries	0.0
Operating expenses
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	149.4
Net Gain on Disposition of Subsidiaries	(178.4)
Repositioning Actions and Net Gain on Disposition of Subsidiaries	(29.0)
Income tax expense
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	(36.0)
Net Gain on Disposition of Subsidiaries	11.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries	(25.0)
Noncontrolling interests
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning Actions	0.0
Net Gain on Disposition of Subsidiaries	6.9
Repositioning Actions and Net Gain on Disposition of Subsidiaries	6.9
Severance
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning actions, liability	25.9
Office lease consolidation and termination
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Repositioning actions, liability	$ 53.0