Commitments and Contingencies, Legal Contingencies (Details) (SPS [Member], Exelon Wind Complaint, USD $)	Mar. 31, 2015 Site Dispute
SPS [Member] \| Exelon Wind Complaint
Legal Contingencies [Abstract]
Number of main areas of dispute	2
Number of wind facilities	12
Accrual for legal contingency	$ 0

Amount of loss contingency liability.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant