Balance Sheet Components Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 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	4	6
Other	7	6
Total regulatory liabilities	11	12
Noncurrent Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	706	692
Asset retirement obligations	40	39
Power cost adjustment mechanism	0	0
Other	36	34
Total regulatory liabilities	782	765
Current Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	80	123
Pension and other postretirement plans	0	0
Deferred income taxes	0	0
Deferred broker settlements	15	20
Debt reacquisition costs	0	0
Deferred capital projects	0	0
Other	1	1
Total regulatory assets	96	144
Noncurrent Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	77	71
Pension and other postretirement plans	314	321
Deferred income taxes	78	80
Deferred broker settlements	1	1
Debt reacquisition costs	20	22
Deferred capital projects	19	16
Other	15	13
Total regulatory assets	$ 524	$ 524