Restructuring Costs Restructuring Liability (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Liability	$ 2.2	$ 19.5
Costs incurred and charged to expense	11.0
Costs paid or otherwise settled	(28.3)
Office lease Termination Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Liability	0.0	0.0
Costs incurred and charged to expense	0.6
Costs paid or otherwise settled	(0.6)
Accelerated Share Based Compensation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Liability	0.0	0.0
Costs incurred and charged to expense	11.3
Costs paid or otherwise settled	(11.3)
Retention Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Liability	2.6	10.8
Costs incurred and charged to expense	15.4
Costs paid or otherwise settled	(23.6)
Pension curtailment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Liability	0.0	0.0
Costs incurred and charged to expense	(0.4)
Costs paid or otherwise settled	0.4
Total [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Liability	4.8	$ 30.3
Costs incurred and charged to expense	37.9
Costs paid or otherwise settled	$ (63.4)