Asset Impairment Expense (Details) - Disposal Groups, Including Discontinued Operations, Name [Domain]	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) project	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) project	Jun. 30, 2014 USD ($)	Mar. 31, 2014 MW
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 37,000,000	$ 63,000,000	$ 45,000,000	$ 75,000,000
UK Wind Development Projects [Domain]
Asset Impairment Expense [Line Items]
number of projects no longer being pursued | project	2
number of impaired projects | project	4		4
Long-Lived Assets	$ 38,000,000		$ 38,000,000
Impairment of Long-Lived Assets Held-for-use	37,000,000		37,000,000
Assets, fair value	1,000,000		1,000,000
East Bend DPL [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	0	0	0	12,000,000
Generation Capacity Mega Watts | MW					186
Assets, fair value		2,000,000		2,000,000
Ebute [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	0	52,000,000	0	52,000,000
Assets, fair value		47,000,000		47,000,000
UK Wind (Newfield) [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use		11,000,000		11,000,000
Assets, fair value		0		0
Other Impairment [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 0	$ 0	$ 8,000,000	$ 0