v2.4.0.6

Summary of significant accounting policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred financing costs
Net carrying amount of deferred financing cost	$ 47.2	$ 40.7
Amortization expenses	4.4	1.3	1.2
Property, plant and equipment
Estimated useful lives	45 years
Project Development Costs and Capitalized Interest
Capitalized interest	$ 17.0	$ 3.0	$ 5.0
Transmission system rights
Transmission system rights
Right to use percentage of Path 15 transmission line in California	72.00%
Regulatory life	30 years
Maximum
Deferred financing costs
Amortization period	28 years
Impairment of long-lived assets, non-amortizing intangible assets and equity method investments
Maximum percentage of ownership in entities in which consolidation is not required	50.00%
Investments accounted for by the equity method
Percentage of investments in partnerships and limited liability companies in which the entity is having the ability to exercise significant influence over operating and financial policies	50.00%
Maximum | Capitalized maintenance costs
Property, plant and equipment
Estimated useful lives	6 years
Minimum
Deferred financing costs
Amortization period	5 years
Investments accounted for by the equity method
Percentage of investments in partnerships and limited liability companies in which the entity is having the ability to exercise significant influence over operating and financial policies	5.00%
Minimum | Capitalized maintenance costs
Property, plant and equipment
Estimated useful lives	3 years

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Represents the period for amortization of deferred financing costs over the term of the related debt.

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The maximum investment ownership percentage for which consolidation is not required.

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Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 8

-Article 9



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Net amount of long-term deferred finance costs capitalized at the end of the reporting period.

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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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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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