Consolidation Of Variable Interest Entities (Carrying Amounts and Classifications of Assets and Liabilities Related to Consolidated VIEs) (Details) (USD $) In Millions, unless otherwise specified					9 Months Ended			9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2013 Consolidated VIEs [Member] Nuclear_generation_units	Dec. 31, 2012 Consolidated VIEs [Member]	Sep. 30, 2013 Texas Competitive Electric Holdings Company LLC [Member]	Sep. 30, 2013 Texas Competitive Electric Holdings Company LLC [Member] Consolidated VIEs [Member]	Sep. 30, 2013 MHI [Member] Consolidated VIEs [Member]
Variable Interest Entity [Line Items]
Number of new nuclear generation units in development (in nuclear generation units)					2
Variable interest entity, ownership percentage (as a percent)								88.00%	12.00%
Assets:
Cash and cash equivalents	$ 1,262	$ 1,175	$ 309	$ 120	$ 37	$ 43	$ 1,300
Accounts receivable	796	710			573	445
Property, plant and equipment	17,961	18,556			138	134
Other assets, including $3 million and $12 million of current assets					12	16
Other current assets	34	120			3	12
Total assets	30,894	32,973			760	638
Liabilities:
Short-term borrowings	2,226	2,136			172	82
Trade accounts payable	354	389			1	1
Other current liabilities	219	255			13	7
Total liabilities	$ 41,537	$ 43,367			$ 186	$ 90