Employee Benefits - Accumulated Benefit Obligations (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 2,804.9	$ 3,057.7
Information for pension plans with an accumulated benefit obligation in excess of plan assets
Projected benefit obligation	1,930.8	679.5
Accumulated benefit obligation	1,882.2	630.3
Fair value of plan assets	$ 1,572.7	$ 339.6