Asset Impairment Expense (Impairment of Long-Lived Assets Held and Used by Asset) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 09, 2013	Dec. 31, 2013	Sep. 30, 2013	Jun. 28, 2012
Debt Instrument [Line Items]
Asset impairment expense	$ 91	$ 95	$ 73
Ebute
Debt Instrument [Line Items]
Asset impairment expense	67	0	0
UK Wind (Newfield)
Debt Instrument [Line Items]
Asset impairment expense	12	0	0
DP&L (East Bend)
Debt Instrument [Line Items]
Asset impairment expense	12	0	0
Beaver Valley
Debt Instrument [Line Items]
Asset impairment expense	0	46	0	46
Conesville (DP&L)
Debt Instrument [Line Items]
Asset impairment expense	0	26	0		26
Itabo (San Lorenzo)
Debt Instrument [Line Items]
Asset impairment expense	0	16	0			16
U.S. wind turbines and projects
Debt Instrument [Line Items]
Asset impairment expense	0	0	41
Kelanitissa
Debt Instrument [Line Items]
Asset impairment expense	0	0	19
St. Patrick
Debt Instrument [Line Items]
Asset impairment expense	0	0	11				11
Other
Debt Instrument [Line Items]
Asset impairment expense	$ 0	$ 7	$ 2