Commitments and Contingencies, Environmental Contingencies (Details) $ in Millions	Dec. 31, 2018 USD ($)
Manufactured Gas Plant (MGP) Sites [Abstract]
Number of Identified MGP Sites Under Current Investigation and/or Remediation	3
Accrual for Environmental Loss Contingencies, Gross	$ 0.6
Federal Coal Ash Regulation [Domain]
Environmental Requirements [Abstract]
Number of sites where statistically significant increases over established groundwater standards exist	2
Number of regulated ash units that will still be in operation by the end of 2019	6
Clean Water Act Effluent Limitations Guidelines [Domain]
Environmental Requirements [Abstract]
Liability for estimated cost to comply with regulation	$ 1.5