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Commitments, Guarantees and Contingencies - Environmental Matters (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Boswell Unit 4 [Member]
Environmental Matters [Line Items]
minimum amount expected to be invested for compliance costs	$ 300
maximum amount expected to be invested for compliance costs	400
Manufactured Gas Plant Site [Member]
Environmental Matters [Line Items]
Liability for Remediation of Manufactured Gas Plant Site	$ 0.5

X

- Definition

The maximum amount expected to be invested for compliance costs for the MATS Rule.

+ References

No definition available.

+ Details

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X

- Definition

The minimum amount expected to be invested for compliance costs of the MATS Rule.

+ References

No definition available.

+ Details

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X

- Details

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X

- Definition

Carrying amount of the liability for remediation of environmental damage pertaining to assets or businesses previously disposed.

+ References

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section Y

-Paragraph Question 4



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 5.Y.Q4)

-URI http://asc.fasb.org/extlink&oid=6572457&loc=d3e149879-122751

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