Business and Organization - Revisions to Comprehensive Income Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net earnings	$ 132.9	$ 71.5	$ 156.1
Comprehensive income	144.3	72.6	132.3
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net earnings	134.0	79.5	157.1
Comprehensive income	145.4	80.6	133.3
Computation of Income Tax Expense | Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net earnings	(1.1)	(8.0)	(1.0)
Comprehensive income	$ (1.1)	$ (8.0)	$ (1.0)