Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Restricted Cash and Cash Equivalents Items [Line Items]
Held-to-maturity Securities, Restricted	$ 24		$ 25
Current	142		193
Non-current	57		60
Total	199		253
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Cash and cash equivalents subject to project finance facilities and lease agreements	176		131
Interest Costs Capitalized	12	8
Inventory	299		301
Treasury Stock, Value, Acquired, Cost Method	75
Adjustments Related to Tax Withholding for Share-based Compensation	6
Debt Service
Restricted Cash and Cash Equivalents Items [Line Items]
Current	11		11
Non-current	41		41
Total	52		52
Rent Reserve
Restricted Cash and Cash Equivalents Items [Line Items]
Current	3		0
Non-current	0		0
Total	3		0
Construction Major Maintenance
Restricted Cash and Cash Equivalents Items [Line Items]
Current	30		32
Non-current	10		14
Total	40		46
Security Project Insurance
Restricted Cash and Cash Equivalents Items [Line Items]
Current	69		101
Non-current	3		3
Total	72		104
Other
Restricted Cash and Cash Equivalents Items [Line Items]
Current	29		49
Non-current	3		2
Total	32		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		3
Cash Flow Statement [Member]
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract]
Prior Period Reclassification Adjustment		$ 4