Balance Sheet Components Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	$ 0	$ 0
Asset retirement obligations	0	0
Power cost adjustment mechanism	3	6
Other	4	6
Total regulatory liabilities	7	12
Noncurrent Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	720	692
Asset retirement obligations	38	39
Power cost adjustment mechanism	0	0
Other	38	34
Total regulatory liabilities	796	765
Current Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	101	123
Pension and other postretirement plans	0	0
Deferred income taxes	0	0
Deferred broker settlements	9	20
Debt reacquisition costs	0	0
Deferred capital projects	0	0
Other	4	1
Total regulatory assets	114	144
Noncurrent Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	77	71
Pension and other postretirement plans	308	321
Deferred income taxes	76	80
Deferred broker settlements	1	1
Debt reacquisition costs	19	22
Deferred capital projects	24	16
Other	14	13
Total regulatory assets	$ 519	$ 524