Fair Value of Financial Instruments Financial Assets and Liabilities Recognized at Fair Value (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Estimate of Fair Value, Fair Value Disclosure [Member]
Nuclear decommissioning trust: (1)
Money market funds	$ 59	$ 59
Debt securities:
Domestic government	14	14
Corporate credit	10	9
Equity securities:
Domestic	7	7
International		1
Debt securities - domestic government	1	1
Assets from price risk management activities: (1) (3)
Electricity	4	10
Natural gas	17	4
Total	112	105
Liabilities from price risk management activities: (1) (3)
Electricity	135	127
Natural gas	43	63
Total	178	190
Fair Value, Inputs, Level 1 [Member]
Nuclear decommissioning trust: (1)
Money market funds	0	0
Debt securities:
Domestic government	8	6
Corporate credit	0	0
Equity securities:
Domestic	5	4
International		1
Debt securities - domestic government	1	1
Assets from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	14	12
Liabilities from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	0	0
Fair Value, Inputs, Level 2 [Member]
Nuclear decommissioning trust: (1)
Money market funds	59	59
Debt securities:
Domestic government	6	8
Corporate credit	10	9
Equity securities:
Domestic	2	3
International		0
Debt securities - domestic government	0	0
Assets from price risk management activities: (1) (3)
Electricity	4	9
Natural gas	16	4
Total	97	92
Liabilities from price risk management activities: (1) (3)
Electricity	20	10
Natural gas	26	40
Total	46	50
Fair Value, Inputs, Level 3 [Member]
Nuclear decommissioning trust: (1)
Money market funds	0	0
Debt securities:
Domestic government	0	0
Corporate credit	0	0
Equity securities:
Domestic	0	0
International		0
Debt securities - domestic government	0	0
Assets from price risk management activities: (1) (3)
Electricity	0	1
Natural gas	1	0
Total	1	1
Liabilities from price risk management activities: (1) (3)
Electricity	115	117
Natural gas	17	23
Total	$ 132	$ 140