Supplementary Financial Information (Asset Retirement and Mining Reclamation Obligations) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Asset Retirement Obligations [Line Items]
Less amounts due currently	$ (60)
Noncurrent liability at September 30, 2013	444	452
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	536
Additions:
Accretion	41
Reductions:
Payments	(73)
Ending balance, Liability	504
Nuclear Plant Decommissioning [Member]
Asset Retirement Obligations [Line Items]
Less amounts due currently	0
Noncurrent liability at September 30, 2013	385
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	368
Additions:
Accretion	17
Reductions:
Payments	0
Ending balance, Liability	385
Mining Land Reclamation [Member]
Asset Retirement Obligations [Line Items]
Less amounts due currently	(60)
Noncurrent liability at September 30, 2013	26
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	135
Additions:
Accretion	23
Reductions:
Payments	(72)
Ending balance, Liability	86
Other
Asset Retirement Obligations [Line Items]
Less amounts due currently	0
Noncurrent liability at September 30, 2013	33
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	33
Additions:
Accretion	1
Reductions:
Payments	1
Ending balance, Liability	$ 33