Asset Impairment Expense (Narrative) (Details) (USD $)	12 Months Ended			3 Months Ended		0 Months Ended	3 Months Ended		1 Months Ended	6 Months Ended
	Dec. 31, 2014 MW	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2014	Mar. 31, 2014	Jan. 09, 2013 MW	Dec. 31, 2013 MW	Sep. 30, 2013 MW	Jun. 30, 2013	Jun. 28, 2012
Debt Instrument [Line Items]
Production Capacity (MW)	2,072
Other Asset Impairment Charges	$ 91,000,000	$ 95,000,000	$ 73,000,000
Gain (loss) on sale of assets	20,000,000	(40,000,000)	(45,000,000)
Ebute
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use				67,000,000
Assets, fair value	36,000,000
Production Capacity (MW)								294
Other Asset Impairment Charges	67,000,000	0	0
UK Wind (Newfield)
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use				12,000,000
Assets, fair value				0
Other Asset Impairment Charges	12,000,000	0	0
DP&L (East Bend)
Debt Instrument [Line Items]
Impairment of Long-Lived Assets Held-for-use					12,000,000
Assets, fair value	2,000,000
Production Capacity (MW)	186
Other Asset Impairment Charges	12,000,000	0	0
Beaver Valley
Debt Instrument [Line Items]
Production Capacity (MW)						125
Lump sum payment received for termination of PPA						60,000,000
Other Asset Impairment Charges	0	46,000,000	0			46,000,000
Conesville (DP&L)
Debt Instrument [Line Items]
Assets, fair value		0					0
Production Capacity (MW)		129					129
Other Asset Impairment Charges	0	26,000,000	0				26,000,000
Itabo (San Lorenzo)
Debt Instrument [Line Items]
Assets, fair value								7,000,000
Production Capacity (MW)								35
Other Asset Impairment Charges	0	16,000,000	0					16,000,000
Assets carrying amount								23,000,000
U.S. wind turbines and projects
Debt Instrument [Line Items]
Assets, fair value									0
Other Asset Impairment Charges	0	0	41,000,000
Gain (loss) on sale of assets									2,000,000
Kelanitissa
Debt Instrument [Line Items]
Other Asset Impairment Charges	0	0	19,000,000
St. Patrick
Debt Instrument [Line Items]
Assets, fair value										22,000,000
Other Asset Impairment Charges	0	0	11,000,000							11,000,000
Assets carrying amount										33,000,000
Long Lived Assets Held And Used | Carrying Amount | Ebute
Debt Instrument [Line Items]
Assets, fair value	103,000,000
Long Lived Assets Held And Used | Carrying Amount | UK Wind (Newfield)
Debt Instrument [Line Items]
Assets, fair value	11,000,000
Long Lived Assets Held And Used | Carrying Amount | DP&L (East Bend)
Debt Instrument [Line Items]
Assets, fair value	14,000,000
Long Lived Assets Held And Used | Carrying Amount | Beaver Valley
Debt Instrument [Line Items]
Assets, fair value		61,000,000					61,000,000
Long Lived Assets Held And Used | Carrying Amount | Conesville (DP&L)
Debt Instrument [Line Items]
Assets, fair value		26,000,000					26,000,000
Long Lived Assets Held And Used | Carrying Amount | Itabo (San Lorenzo)
Debt Instrument [Line Items]
Assets, fair value		23,000,000					23,000,000
Fair Value, Inputs, Level 3 [Member] | Fair Value
Debt Instrument [Line Items]
Assets, fair value	309,000,000
Fair Value, Inputs, Level 3 [Member] | Long Lived Assets Held And Used | Fair Value | Ebute
Debt Instrument [Line Items]
Assets, fair value	36,000,000
Fair Value, Inputs, Level 3 [Member] | Long Lived Assets Held And Used | Fair Value | UK Wind (Newfield)
Debt Instrument [Line Items]
Assets, fair value	0
Fair Value, Inputs, Level 3 [Member] | Long Lived Assets Held And Used | Fair Value | Beaver Valley
Debt Instrument [Line Items]
Assets, fair value		15,000,000					15,000,000
Fair Value, Inputs, Level 3 [Member] | Long Lived Assets Held And Used | Fair Value | Conesville (DP&L)
Debt Instrument [Line Items]
Assets, fair value		0					0
Fair Value, Inputs, Level 3 [Member] | Long Lived Assets Held And Used | Fair Value | Itabo (San Lorenzo)
Debt Instrument [Line Items]
Assets, fair value		$ 7,000,000					$ 7,000,000