Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges	$ 0us-gaap_FairValueHedgesAtFairValueNet	$ 0us-gaap_FairValueHedgesAtFairValueNet	$ 0us-gaap_FairValueHedgesAtFairValueNet
Recognized gains (losses) from fair value hedges or related hedged transactions	0	0	0
Cash Flow Hedges [Member] \| Interest Rate [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		300,000	300,000
Designated as Hedging Instrument [Member] \| Cash Flow Hedges [Member] \| Interest Rate [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	300,000
Other Derivative Instruments [Member] \| Electric Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities	(3,900,000)	9,900,000
Derivative Instruments Gain Loss Reclassified To Regulatory Assets And Liabilities Net	$ 8,200,000

Derivative Instruments Gain Loss Reclassified To Regulatory Assets And Liabilities Net

No definition available.

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in regulatory assets and liabilities during the current period.

+ References

No definition available.

+ Details

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- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4D

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624177-113959

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- Definition

Net fair value of all derivative instruments designated as fair value hedging instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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- Definition

Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period.

+ References

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