Regulatory Assets, Liabilities, and Balancing Accounts (Regulatory Balancing Accounts, Net) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Current regulatory balancing accounts, net	$ 961	$ 849
Utility Generation [Member]
Current regulatory balancing accounts, net	460	303
Distribution Revenue Adjustment Mechanism [Member]
Current regulatory balancing accounts, net	378	145
Public Purpose Programs [Member]
Current regulatory balancing accounts, net	129	164
Hazardous Substance [Member]
Current regulatory balancing accounts, net	57	38
Gas Fixed Cost [Member]
Current regulatory balancing accounts, net	(23)	56
Energy Procurement Costs [Member]
Current regulatory balancing accounts, net	(137)	(25)
Energy Recovery Bonds [Member]
Current regulatory balancing accounts, net	(126)	(34)
Other Current Balancing Accounts [Member]
Current regulatory balancing accounts, net	$ 223	$ 202