Acadia Transactions (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011
Acadia Unit 1 and Facilities [Member] \| APH [Member]
Significant Acquisitions and Disposals [Line Items]
Indemnification against third parties	$ 6.8
Third parties' share of entity's liabilities (in hundredths)	50.00%
APH [Member] \| Acadia Unit 2 and Facilities [Member]
Significant Acquisitions and Disposals [Line Items]
Recognized gain on transaction	62.0
Indemnification against third parties	10.9
Third parties' share of entity's liabilities (in hundredths)	50.00%
Net adjustment to equity income	26.2
Impairment of investment	45.9
Capitalized interest and other	19.7
Acadia Unit 1 and Facilities [Member] \| Acadia Power Partners [Member]
Significant Acquisitions and Disposals [Line Items]
Recognized gain on transaction	82.0
Acadia Unit 1 and Facilities [Member]
Significant Acquisitions and Disposals [Line Items]
Value of plant acquisition	304.0
Deferred taxes recognized	78.4
Acadia Unit 2 and Facilities [Member]
Significant Acquisitions and Disposals [Line Items]
Value of plant acquisition	$ 298.8

Capitalized interest and other in the investee on the equity method of accounting, from inception to date.

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- Definition

Amount of deferred tax liability for the differences between the values assigned and the tax bases of assets in an asset acquisition.

+ Details

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- Definition

Impairment of investment in the investee on the equity method of accounting from inception to date.

+ Details

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- Definition

The amount of indemnification liability recognized at the acquisition date.

+ Details

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- Definition

This item represents a net adjustment to the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

+ Details

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- Definition

The third parties' share of entity's liabilities and other obligations.

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- Definition

The value of all consideration given or received by the Entity in the significant acquisition or disposal.

+ Details

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- Definition

The difference between the value of the consideration received by the Entity on the sale or disposal and the consideration received by the Entity, including any tax related impact.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2941-110230

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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