Balance Sheet Components Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Current Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	$ 39	$ 26
Pension and other postretirement plans	0	0
Deferred income taxes	0	0
Debt issuance costs	0	0
Other	3	10
Total regulatory assets	42	36
Noncurrent Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	150	120
Pension and other postretirement plans	225	235
Deferred income taxes	83	86
Debt issuance costs	20	22
Other	48	35
Total regulatory assets	526	498
Current Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	0	0
Trojan decommissioning activities	4	18
Asset retirement obligations	0	0
Other	16	33
Total regulatory liabilities	20	51
Noncurrent Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	921	887
Trojan decommissioning activities	0	0
Asset retirement obligations	52	49
Other	29	22
Total regulatory liabilities	$ 1,002	$ 958