Contingent Liabilities and Commitments (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Oct. 09, 2019	Dec. 31, 2018	Dec. 20, 2018	Jul. 29, 2016
Commitments and Contingencies Disclosure [Abstract]
Reserve for rate refund	$ 130.8
Subsequent Event [Member]
Site Contingency [Line Items]
Payment of penalty		$ 1.4
Environmental assessment and remediation [Member]
Site Contingency [Line Items]
Accrued environmental assessment and remediation costs, total	3.0		$ 3.5
Accrued environmental assessment and remediation costs, current	1.3		1.5
Accrued environmental assessment and remediation costs, noncurrent	1.7		$ 2.0
Potentially responsible party at various Superfund and state waste disposal sites [Member] | Maximum [Member]
Site Contingency [Line Items]
Site Contingency, Loss Exposure Not Accrued, Best Estimate	$ 0.5
Accrued Liabilities
Site Contingency [Line Items]
Notice of Penalty				$ 1.4	$ 1.6