Balance Sheet Components Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Current Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	$ 41	$ 26
Pension and other postretirement plans	0	0
Deferred income taxes	0	0
Debt issuance costs	0	0
Other	6	10
Total regulatory assets	47	36
Noncurrent Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	156	120
Pension and other postretirement plans	229	235
Deferred income taxes	82	86
Debt issuance costs	20	22
Other	49	35
Total regulatory assets	536	498
Current Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	0	0
Trojan decommissioning activities	8	18
Asset retirement obligations	0	0
Other	26	33
Total regulatory liabilities	34	51
Noncurrent Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	910	887
Trojan decommissioning activities	0	0
Asset retirement obligations	51	49
Other	28	22
Total regulatory liabilities	$ 989	$ 958