Contingent Liabilities and Commitments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Environmental Matters
Environmental assessment and remediation costs, undiscounted	$ 3.0
Accrued environmental liabilities	3.0	$ 4.4
Accrued Environmental Loss Contingencies, Current	1.3	1.3
Accrued Environmental Loss Contingencies, Noncurrent	$ 1.7	$ 3.1