Benefit Plans - Pension and Other Post-retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets	$ 180.7	$ 382.8
Pension plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit obligation	277.9	473.8	$ 423.8
Plan assets	180.7	$ 382.8	$ 352.3
Pension plans | Salaried Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Lump-sum payments	$ 171.9
Period of annuity purchase	120 days
Benefit obligation	$ 175.9
Plan assets	$ 153.7