Goodwill and Other Intangible Assets (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 18, 2015
Goodwill [Line Items]
Goodwill impairment expense		$ 0	$ 0	$ 317
Goodwill		1,059	1,157
Goodwill		3,814	$ 3,912
Main street power [Member]
Goodwill [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired					100.00%
DPL Subsidiary [Member]
Goodwill [Line Items]
Goodwill impairment expense	$ 317
Goodwill		$ 317