v2.4.0.8

Acquisitions and divestments (Details) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended	0 Months Ended			1 Months Ended			0 Months Ended		1 Months Ended			1 Months Ended			0 Months Ended	3 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended
	Sep. 30, 2012	May 02, 2013 Canadian Hills	Jul. 31, 2012 Canadian Hills	Mar. 30, 2012 Canadian Hills	Dec. 31, 2012 Canadian Hills item	Sep. 30, 2013 Canadian Hills	Jan. 31, 2012 Canadian Hills MW	Apr. 12, 2013 Auburndale, Lake and Pasco	Jan. 30, 2013 Auburndale, Lake and Pasco	Apr. 30, 2013 Auburndale, Lake and Pasco	Apr. 30, 2013 Path 15	Sep. 30, 2013 Path 15	May 31, 2012 Primary Energy Recycling Corporation	Feb. 29, 2012 Primary Energy Recycling Corporation	Feb. 16, 2012 Primary Energy Recycling Corporation	Apr. 02, 2013 Gregory	Sep. 30, 2013 Gregory	Sep. 30, 2013 Gregory	Sep. 04, 2012 Badger Creek	Jun. 30, 2012 Badger Creek
Acquisition and divestments
Percentage acquired in entity				48.00%			51.00%
Wind power project capacity (in MW)							300
Percentage of ownership interest				99.00%											14.30%				50.00%
Percentage of retained interest				1.00%
Project-level construction financing facility				$ 310.0								$ 137.2
Construction loan				290.0
Letter of credit facility				20.0
Letter of credit facility, term				5 years
Investment in equity			190
Tax equity investments received					225
Number of institutional tax equity investors by whom tax equity investments received					4
Own tax equity investment		44			44
Interest sold (as a percent)		100.00%
Tax equity interests		269
Short-term debt					265	0
Proceeds from sale of remaining tax equity ownership		42.1						92.0		25.0
Total price									140.0		56.0			30.2		274.2
Expected proceeds from sale																34.6
Proceeds from sale to be held in escrow account																5
Term Of Escrow Account																1 year
Net cash proceeds from sale	27.9							117.0			52.0								3.7
Management termination fee											4.0			6.0
Outstanding balance of senior credit facility								64.1
Impairment charge on pending sale																				3.0
Price of entity's common membership interest in equity method investee														24.2
Gain on sale of equity method investment													$ 0.6				$ 30.4	$ 30.4
Entity's common membership interest to be purchased in equity method investee (in shares)														7,462,830

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Represents the amount of sales proceeds received on disposal of the common membership interest in an equity method investment.

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No definition available.

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Represents the number of shares to be purchased on disposal of the common membership interest in an equity method investment.

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Represents the amount of management termination fee received on disposal of an equity method investment.

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Represents the percentage of investment sold, accounted under the equity method of accounting.

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No definition available.

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Represents the percentage of interest retained by an entity.

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Represents the expected cash inflow associated with the sale of equity method investments.

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Represents the number of institutional tax equity investors by whom tax equity investments were received.

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The expected cash inflow associated with the sale of equity method investments to be held in escrow account for specified period of time.

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Represents the amount of tax equity investment including entity's owned tax investment.

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Represents the amount of the entity's owned tax investment.

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Represents the amount of tax equity investments received during the period.

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Represents the maximum term of escrow account.

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Represents the capacity of wind power project.

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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This element represents the carrying value of a short-term real estate loan to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project, usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property. Note that there are separate concepts for the current and noncurrent portions of long-term construction loans.

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This item represents the amount of net sales proceeds received on disposal of an equity method investment.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of gain (loss) on sale or disposal of an equity method investment.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Amount borrowed under the credit facility as of the balance sheet date.

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This element represents the current and noncurrent portions of a long-term real estate loan with an initial maturity beyond one year or beyond the normal operating cycle, if longer, to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project (generally one to seven years), usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property.

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The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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