Contingent Liabilities and Commitments (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Site Contingency [Line Items]
Environmental assessment and remediation costs, undiscounted	$ 2.9
Environmental Restoration Costs [Member]
Site Contingency [Line Items]
Accrued environmental assessment and remediation costs, total	2.9	$ 3.0
Accrued environmental assessment and remediation costs, current	1.3	1.3
Accrued environmental assessment and remediation costs, noncurrent	$ 1.6	$ 1.7