Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012	Dec. 31, 2012
Restricted Cash and Cash Equivalents Items [Line Items]
Held-to-maturity Securities, Restricted	$ 24			$ 24			$ 25
Current	140			140			193
Non-current	58			58			60
Total	198			198			253
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Cash and cash equivalents subject to project finance facilities and lease agreements	127			127			131
Interest Costs Capitalized	12		9	24		17
Inventory	345			345			301
Treasury Stock, Value, Acquired, Cost Method				362
Adjustments Related to Tax Withholding for Share-based Compensation				6
Debt Service
Restricted Cash and Cash Equivalents Items [Line Items]
Current	14	[1]		14	[1]		11	[1]
Non-current	42	[1]		42	[1]		41	[1]
Total	56	[1]		56	[1]		52	[1]
Rent Reserve
Restricted Cash and Cash Equivalents Items [Line Items]
Current	7			7			0
Non-current	0			0			0
Total	7			7			0
Construction Major Maintenance
Restricted Cash and Cash Equivalents Items [Line Items]
Current	26			26			32
Non-current	8			8			14
Total	34			34			46
Security Project Insurance
Restricted Cash and Cash Equivalents Items [Line Items]
Current	73			73			101
Non-current	6			6			3
Total	79			79			104
Other
Restricted Cash and Cash Equivalents Items [Line Items]
Current	20			20			49
Non-current	2			2			2
Total	22			22			51
Geothermal Properties, Gross [Member] | Minimum [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Estimated Useful Lives				13 years
Geothermal Properties, Gross [Member] | Maximum [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Estimated Useful Lives				59 years
Property, Plant and Equipment, Other Types [Member] | Minimum [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Estimated Useful Lives				3 years
Property, Plant and Equipment, Other Types [Member] | Maximum [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Estimated Useful Lives				47 years
Building, Machinery and Equipment, Gross [Member] | Minimum [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Estimated Useful Lives				3 years
Building, Machinery and Equipment, Gross [Member] | Maximum [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Estimated Useful Lives				47 years
Income Statement [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Prior Period Reclassification Adjustment			2			5
Cash Flow Statement [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Prior Period Reclassification Adjustment						$ 3

[1] June 30, 2013 and December 31, 2012, amounts restricted for debt service included approximately $24 million and $25 million, respectively, of repurchase agreements with a financial institution containing maturity dates greater than one year.In