Goodwill Impairment (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Goodwill [Line Items]
Goodwill impairment expense	$ 154,000,000	$ 0
DPLER [Member]
Goodwill [Line Items]
Goodwill	136,000,000
Goodwill implied fair value	0
Goodwill impairment expense	136,000,000
Buffalo Gap [Member]
Goodwill [Line Items]
Goodwill impairment expense	$ 18,000,000
Number of wind projects	3
Generation capacity mega watts	524