Balance Sheet Components Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Current Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	$ 50	$ 26
Pension and other postretirement plans	0	0
Deferred income taxes	0	0
Debt issuance costs	0	0
Other	7	10
Total regulatory assets	57	36
Noncurrent Regulatory Assets [Member]
Regulatory Assets and Liabilities [Line Items]
Price risk management	154	120
Pension and other postretirement plans	232	235
Deferred income taxes	83	86
Debt issuance costs	21	22
Other	42	35
Total regulatory assets	532	498
Current Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	0	0
Trojan decommissioning activities	12	18
Asset retirement obligations	0	0
Other	30	33
Total regulatory liabilities	42	51
Noncurrent Regulatory Liabilities [Member]
Regulatory Assets and Liabilities [Line Items]
Asset retirement removal costs	898	887
Trojan decommissioning activities	0	0
Asset retirement obligations	50	49
Other	25	22
Total regulatory liabilities	$ 973	$ 958