Commitments, Guarantees and Contingencies - Environmental Matters (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Boswell Unit 4 [Member]
Environmental Matters [Line Items]
Estimated Capital Expenditures	$ 260
Capital Cost Spent to Date	162
Maximum [Member] \| Clean Water Act - Aquatic Organisms [Member]
Environmental Matters [Line Items]
Estimated Environmental Compliance Costs	15
Maximum [Member] \| Coal Combustion Residuals [Member]
Environmental Matters [Line Items]
Estimated Environmental Compliance Costs	130
NOV Consent Decree [Member]
Environmental Matters [Line Items]
Generating Unit Capacity (MW)	200.0
NOV Consent Decree [Member] \| Minimum [Member]
Environmental Matters [Line Items]
Estimated Capital Expenditures	20
NOV Consent Decree [Member] \| Maximum [Member]
Environmental Matters [Line Items]
Estimated Capital Expenditures	$ 40

Capital cost spent to date for project.

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- Definition

The estimated amount of certain future capital expenditures related to environmental compliance, regulatory matters, or other committments and/or contingencies.

+ References

No definition available.

+ Details

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The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period.

+ References

No definition available.

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Capacity of a generating facility, unit, or project in megawatts.

+ References

No definition available.

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- Definition

Best estimate of the loss exposure for reasonably possible environmental contingencies at an individual site for which no accrual has been recorded.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 10

-Subparagraph (c),(d)(2)

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

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