Restructuring Costs Restructuring Expense Table (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Accelerated share-based compensation	$ 3.2		$ 7.2
Termination Benefits [Member]
Costs recognized period from inception to September 30, 2018	13.7	$ 13.7
Total remaining costs expected to be incurred		0.0
Office lease Termination Costs [Member]
Costs recognized period from inception to September 30, 2018	1.0	1.0
Total remaining costs expected to be incurred		0.0
Accelerated Share Based Compensation [Member]
Costs recognized period from inception to September 30, 2018	7.2	7.2
Total remaining costs expected to be incurred		0.0
Retention Expense [Member]
Costs recognized period from inception to September 30, 2018	13.8	13.8
Total remaining costs expected to be incurred		10.5
Pension curtailment [Member]
Costs recognized period from inception to September 30, 2018	0.3	0.3
Total remaining costs expected to be incurred		0.0
Total [Member]
Termination benefits	6.7	13.7
Office lease termination costs	0.7	1.0
Accelerated share-based compensation	3.2	7.2
Retention expense	5.8	13.8
Pension curtailment	0.3	0.3
Total restructuring costs	16.7	36.0
Costs recognized period from inception to September 30, 2018	36.0	36.0
Total remaining costs expected to be incurred		10.5
General and Administrative Expense [Member]
Termination benefits	5.3	10.4
Office lease termination costs	0.7	1.0
Accelerated share-based compensation	1.0	5.0
Retention expense	5.8	13.8
Pension curtailment	0.0	0.0
Total restructuring costs	12.8	30.2
Net gain (loss) from asset sales [Member]
Termination benefits	1.4	3.3
Office lease termination costs	0.0	0.0
Accelerated share-based compensation	2.2	2.2
Retention expense	0.0	0.0
Pension curtailment	0.0	0.0
Total restructuring costs	3.6	5.5
Interest and other income (expense) [Member]
Termination benefits	0.0	0.0
Office lease termination costs	0.0	0.0
Accelerated share-based compensation	0.0	0.0
Retention expense	0.0	0.0
Pension curtailment	0.3	0.3
Total restructuring costs	$ 0.3	$ 0.3