Asset Retirement Obligations (Details Textuals) (USD $)	12 Months Ended
Dec. 31, 2014
Asset Retirement Obligations [Line Items]
Asset retirement obligations, liability not recognized	Natural gas storage system assets, substations, manholes and certain other distribution assets have an indeterminate life. Therefore, no liability has been recorded for these assets.
Liabilities balance upon completion of decommissioning	$ 0
Fermi 2 [Member]
Asset Retirement Obligations [Line Items]
Nuclear decommissioning liabilities funded through surcharge and included in ARO balance	$ 1,700,000,000

Description of an asset retirement obligation for which a liability has not been recognized because fair value cannot be reasonably estimated and the reasons why fair value cannot be reasonably estimated.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7569-110849

Name:	us-gaap_AssetRetirementObligationsLiabilityNotRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration