Fair Value Disclosures (Realized And Unrealized Gains Or (Losses) On Level 3 Instruments Included In Income As A Component Of Other Income Or Other Operation And Maintenance Expense) (Details) (USD $) In Millions	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Fair Value Disclosures
Total gains included in income for the period	$ 5	$ 2
Change in unrealized gains relating to assets still held at reporting date	$ 2	$ 2