Variable Interest Entities (Projects Not Consolidated) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Domestic Gas and Wind Energy Projects \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity
Ownership interest in unconsolidated affiliate (as a percent)	100.00%
Natural Gas-Fired Projects
Variable Interest Entity
Investment	$ 325
Maximum Exposure	325
Natural Gas-Fired Projects \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity
Number of projects (project)	5	5
Big 4 Projects \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity
Number of projects operated by subsidiary (project)	3
Wind Projects
Variable Interest Entity
Investment	188
Maximum Exposure	188
Domestic Energy Projects \| Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity
Indebtedness of projects accounted for under equity method	25	32
Indebtedness of projects accounted for under equity method, amount proportionate to ownership interest	6	8
Equity Interests
Revenue	754	607	769
Expenses	656	519	601
Net income	98	88	168
Current assets	411	337
Noncurrent assets	657	711
Total assets	1,068	1,048
Current liabilities	120	78
Noncurrent liabilities	72	82
Equity	876	888
Total liabilities and equity	1,068	1,048
Difference between the carrying value of equity investments and the underlying equity	9
Undistributed earnings of equity method investments	$ 18	$ 19

Number of projects in which the entity has an interest.

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Number of Projects Operated by Subsidiary

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The carrying amount of debt for variable interests in projects accounted for under the equity method.

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The entity's proportionate share of the debt for the VIE projects accounted for under the equity method, according to the entity's ownership share.

+ References

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Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

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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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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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The amount of assets reported by an equity method investment of the entity.

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- Definition

The amount of the cost of sales reported by an equity method investment of the entity.

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- Definition

The amount of current assets reported by an equity method investment of the entity.

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The amount of current liabilities reported by an equity method investment of the entity.

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Amount of equity, excluding noncontrolling interest, attributable to the equity method investment of the entity.

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The amount of liabilities and equity reported by an equity method investment of the entity.

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The amount of net income (loss) reported by an equity method investment of the entity.

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The amount of noncurrent assets reported by an equity method investment of the entity.

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The amount of noncurrent liabilities reported by an equity method investment of the entity.

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The amount of revenue from sale of goods and services reduced by sales returns, allowances, and discounts reported by an equity method investment of the entity.

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Amount of consolidated retained earnings that represent undistributed (not yet received) earnings from 50% or less owned persons accounted for by the equity method (equity method investees).

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

-Publisher FASB

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-Topic 852

-SubTopic 20

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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

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-Name FASB Staff Position (FSP)

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- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

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