Supplementary Financial Information (Asset Retirement and Mining Reclamation Obligations) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	$ 614
Additions:
Accretion	38
Adjustment for new cost estimate (a)	70
Incremental reclamation costs (b)	59
Reductions:
Payments	(45)
Ending balance, Liability	614	$ 736	$ 614
Less amounts due currently		(65)
Noncurrent liability at September 30, 2015		671	560
Coal Combustion Residuals [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	59
Reductions:
Ending balance, Liability	59		59
Nuclear Plant Decommissioning [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	413
Additions:
Accretion	19
Adjustment for new cost estimate (a)	70
Incremental reclamation costs (b)	0
Reductions:
Payments	0
Ending balance, Liability	413	502	413
Less amounts due currently		0
Noncurrent liability at September 30, 2015		502
Mining Land Reclamation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	165
Additions:
Accretion	15
Adjustment for new cost estimate (a)	0
Incremental reclamation costs (b)	0
Reductions:
Payments	(44)
Ending balance, Liability	165	136	165
Less amounts due currently		(65)
Noncurrent liability at September 30, 2015		71
Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance, Liability	36
Additions:
Accretion	4
Adjustment for new cost estimate (a)	0
Incremental reclamation costs (b)	59
Reductions:
Payments	(1)
Ending balance, Liability	$ 36	98	$ 36
Less amounts due currently		0
Noncurrent liability at September 30, 2015		$ 98