Pensions and Other Postretirement Benefits (Net Periodic Benefit Costs) (Details) - Pension and other postretirement benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5.0	$ 5.0
Interest cost	3.6	3.7
Expected return on plan assets	(3.6)	(3.5)
Amortization of prior service costs	0.1	0.1
Recognized net actuarial losses	0.0
Net periodic benefit cost	$ 5.1	$ 5.5