Goodwill Impairment (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 DPLER [Member]	Mar. 31, 2014 DPLER [Member]	Mar. 31, 2014 Buffalo Gap [Member] MW project
Goodwill [Line Items]
Goodwill						$ 136,000,000
Goodwill implied fair value						0
Goodwill impairment expense	$ 0	$ 0	$ 154,000,000	$ 0	$ 0	$ 136,000,000	$ 18,000,000
Number of wind projects							3
Generation capacity mega watts							524