Summary of Significant Accounting Policies (Goodwill) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
SoCore Energy
Goodwill [Line Items]
Goodwill impairment	$ 16.5
Goodwill impairment after tax	10.0
Goodwill	5.0	$ 22.0
Edison Energy Group
Goodwill [Line Items]
Goodwill	$ 78.0	$ 78.0