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