Summary of Significant Accounting Policies (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation	$ 31,751	$ 30,121
Transmission	8,240	7,835
Distribution	15,458	14,870
General	3,413	3,116
Plant acquisition adjustment	124	43
Utility plant in service	58,986	55,985
Information technology equipment and software	220	216
Communications equipment	428	423
Other	110	107
Other plant in service	758	746
Total plant in service	$ 59,744	$ 56,731