Regulatory Assets, Liabilities, And Balancing Accounts (Narrative) (Details) (USD $)	Sep. 30, 2011 years	Dec. 31, 2010
Regulatory Assets, Liabilities, And Balancing Accounts [Abstract]
Current regulatory assets	$ 680,000,000	$ 599,000,000
Unrealized losses price risk management derivative instruments period (years)	1
Undepreciated conventional electromechanical meters regulatory assets recovery maximum (years)	6
Deferred income taxes regulatory asset recovery minimum (years)	1
Deferred income taxes regulatory asset recovery maximum (years)	45
Utility retained generation asset costs	1,200,000,000
Utility retained generation asset costs (years)		1
Weighted average remaining life of Utility retained generation assets (years)	13
Environmental compliance costs regulatory asset recovery (years)	32
Price risk management regulatory assets recovery (years)	11
Recovery of costs related to debt reacquired or redeemed prior to maturity (years)	15
Term of a terminated power purchase agreement (years)	30
Current regulatory liabilities	$ 120,000,000	$ 81,000,000
Period of time expected to receive authorized rate adjustments (months)	12
Period of time exceeded for regulatory balancing accounts to be recorded in other noncurrent assets (months)	12
Recovery of remediation costs, percentage	90.00%
Recovery of energy procurement costs, percentage	100.00%