Dispositions of Subsidiaries and Repositioning Actions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries	$ 0.0	$ (178.4)	$ 0.0
Repositioning Actions		149.4
Severance		68.4
Office lease consolidation and termination		73.5
Asset write-offs related to disposals and other costs		7.5
Repositioning actions, liability	$ 25.1	78.9
Salary and service costs
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		0.0
Repositioning Actions		73.7
Repositioning Actions and Net Gain on Disposition of Subsidiaries		73.7
Occupancy and other costs
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		0.0
Repositioning Actions		73.5
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]
Net Gain on Disposition of Subsidiaries		(178.4)
Repositioning Actions		0.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries		(178.4)
Cost of services
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		(178.4)
Repositioning Actions		147.2
Repositioning Actions and Net Gain on Disposition of Subsidiaries		(31.2)
Selling, general and administrative expenses
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		0.0
Repositioning Actions		2.2
Repositioning Actions and Net Gain on Disposition of Subsidiaries		2.2
Depreciation and amortization
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		0.0
Repositioning Actions		0.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries		0.0
Operating expenses
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		(178.4)
Repositioning Actions		149.4
Repositioning Actions and Net Gain on Disposition of Subsidiaries		(29.0)
Income tax expense
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		11.0
Repositioning Actions		(36.0)
Repositioning Actions and Net Gain on Disposition of Subsidiaries		(25.0)
Noncontrolling interests
Dispositions of Subsidiaries and Repositioning Actions [Line Items]
Net Gain on Disposition of Subsidiaries		6.9
Repositioning Actions		0.0
Repositioning Actions and Net Gain on Disposition of Subsidiaries		$ 6.9