Other Investments (Summary of Changes in Fair Value of the Nuclear Decommissioning Trusts) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Summary Of Changes In The Fair Value [Roll Forward]
Balance at beginning of period	$ 3,853	$ 3,619	$ 3,592	$ 3,480
Gross realized gains	15	12	40	35
Gross realized losses	(1)	0	(5)	0
Unrealized gains (losses) - net	(67)	4	116	106
Other-than-temporary impairments	19	4	23	13
Interest, dividends, contributions and other	29	26	90	49
Balance at end of period	$ 3,810	$ 3,657	$ 3,810	$ 3,657