Other Postretirement Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Postretirement liability, noncurrent	$ 1,052.0	$ 1,222.9
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Postretirement liability, noncurrent	$ 152.0	$ 158.0
Medical trend rate - initial	6.30%	6.50%
Medical trend rate - ultimate	4.50%	4.50%
Unrecognized prior service credits, before tax	$ (21.0)
Unrecognized net prior service credits, net of tax	(13.0)
Unrecognized actuarial losses, before tax	(16.0)
Unrecognized actuarial losses, net of tax	(10.0)
Future amortization of prior service cost (credit)	3.0
Future amortization of prior service cost (credit), net of tax	$ 2.0