Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
Sep. 30, 2009	Jun. 30, 2012	Jun. 30, 2012 Regional Transmission Organization Costs [Member] Y
Regulatory asset, amortization period, years			10
Reconciliation period	2
Reduction in recovery of fuel costs		$ 3.3

Discloses the amount of any reduction to the carrying amounts of regulated assets that result from impairment (for example, rate actions of a regulator).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 35

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6066304&loc=d3e44026-110379

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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