Summary of Significant Accounting Policies Property, Plant and Equipment, Net (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Buildings, machinery and equipment	$ 14,783	$ 14,774
Geothermal properties	1,248	1,243
Other	155	142
Property, Plant and Equipment, Gross	16,186	16,159
Less: Accumulated depreciation	4,516	4,390
Property, Plant and Equipment, Gross, Less Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	11,670	11,769
Land	98	98
Construction in progress	1,284	1,138
Property, plant and equipment, net	$ 13,052	$ 13,005