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Summary of Significant Accounting Policies (Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Jun. 30, 2017	Dec. 31, 2017
SoCore Energy
Goodwill [Line Items]
Goodwill impairment		$ 16.5
Goodwill impairment after tax		$ 10.0
Goodwill			$ 5.0
Edison Energy Group
Goodwill [Line Items]
Goodwill impairment	$ 19.0
Goodwill impairment after tax	13.0
Goodwill	59.0		$ 78.0
Edison Energy
Goodwill [Line Items]
Investment	$ 83.0