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Fair Value Measurements (Fair Value of Assets and Liabilities Measured on a Nonrecurring Basis) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2015	Dec. 31, 2014
Carrying Value		$ 2,510,600,000us-gaap_PropertyPlantAndEquipmentNet	$ 2,517,600,000us-gaap_PropertyPlantAndEquipmentNet
Fixed asset impairment	11,500,000
Goodwill		317,000,000us-gaap_Goodwill	317,000,000us-gaap_Goodwill
Goodwill Impairment	135,800,000us-gaap_GoodwillImpairmentLoss
Parent Company [Member]
Fixed asset impairment	11,500,000
Goodwill Impairment	135,800,000
DPLER [Member]
Goodwill	135,800,000
Goodwill Impairment	135,800,000
East Bend Station [Member]
Carrying Value	14,200,000
Fixed asset impairment	11,500,000
Fair Value	2,700,000
East Bend Station [Member] \| Level 3 [Member]
Fair Value	$ 2,700,000