Investments (Marketable Equity and Debt Securities and Cash Equivalents (Classified as Available-for-sale) and Cost Method Investments in Decommissioning Trust Funds) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Available-for-sale Securities, Amortized Cost Basis, and Other Investments	$ 2,390		$ 2,340
Available-for-sale Securities, Total Unrealized Gains	611	[1]	563	[1]
Available-for-sale Securities, Total Unrealized Losses	(2)	[1],[2]	(6)	[1],[2]
Fair Value	2,999		2,897
Net assets related to pending sales and purchases of securities	11		43
Fair value of securities in an unrealized loss position	164		252
Cost-method Investments [Member]
Other Investments and Securities, at Cost	118		108
Available-for-sale Securities, Total Unrealized Gains	0		0
Available-for-sale Securities, Total Unrealized Losses	0		0
Fair Value	118		108
Cash Equivalents and Other Investment [Member]
Other Investments and Securities, at Cost	46	[3]	79	[3]
Available-for-sale Securities, Total Unrealized Gains	0		0
Available-for-sale Securities, Total Unrealized Losses	0		0
Fair Value	46	[3]	79	[3]
Equity Securities [Member] | Large Cap [Member] | United States [Member]
Amortized Cost	1,152		1,161
Available-for-sale Securities, Total Unrealized Gains	537	[1]	515	[1]
Available-for-sale Securities, Total Unrealized Losses	0	[1]	0	[1]
Fair Value	1,689		1,676
Equity Securities [Member] | Other Market [Member] | United States [Member]
Amortized Cost	36		39
Available-for-sale Securities, Total Unrealized Gains	10	[1]	11	[1]
Available-for-sale Securities, Total Unrealized Losses	0	[1]	0	[1]
Fair Value	46		50
Corporate Debt Securities [Member]
Amortized Cost	314		310
Available-for-sale Securities, Total Unrealized Gains	19	[1]	18	[1]
Available-for-sale Securities, Total Unrealized Losses	(1)	[1]	(1)	[1]
Fair Value	332		327
US Government Debt Securities [Member]
Amortized Cost	437		380
Available-for-sale Securities, Total Unrealized Gains	20	[1]	12	[1]
Available-for-sale Securities, Total Unrealized Losses	(1)	[1]	(1)	[1]
Fair Value	456		391
US States and Political Subdivisions Debt Securities [Member]
Amortized Cost	264		244
Available-for-sale Securities, Total Unrealized Gains	24	[1]	7	[1]
Available-for-sale Securities, Total Unrealized Losses	0	[1]	(4)	[1]
Fair Value	288		247
Other Debt Securities [Member]
Amortized Cost	23		19
Available-for-sale Securities, Total Unrealized Gains	1	[1]	0	[1]
Available-for-sale Securities, Total Unrealized Losses	0	[1]	0	[1]
Fair Value	$ 24		$ 19

[1] Included in AOCI and the decommissioning trust regulatory liability as discussed in Note 2.

[2] The fair value of securities in an unrealized loss position was $164 million and $252 million at December 31, 2011 and 2010, respectively.

[3] Includes pending purchases of securities of $11 million and $43 million at December 31, 2011 and 2010, respectively.