Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Remaining Recovery Period of Regulatory Assets, Price Risk Management	4 years
Remaining Recovery Period of Regulatory Asset, Debt Reacquisition Costs	8 years
Price risk management	$ 10	$ 6
Deferred income taxes	$ 42	48
remaining recovery period of regulatory assets, deferred capital projects	1 year
Remaining refund period of regulatory liability, Trojan decommissioning activities	3 years
Current Regulatory Liabilities [Member]
Regulatory Assets [Line Items]
Asset retirement removal costs	$ 0	0
Proceeds from Legal Settlements	17	23
Asset retirement obligations	0	0
Other	38	37
Total regulatory liabilities	55	60
Noncurrent Regulatory Liabilities [Member]
Regulatory Assets [Line Items]
Asset retirement removal costs	837	804
Proceeds from Legal Settlements	15	34
Asset retirement obligations	45	39
Other	31	29
Total regulatory liabilities	928	906
Regulatory Assets, Current [Member]
Regulatory Assets [Line Items]
Price risk management	120	100
Pension and other postretirement plans	0	0
Deferred income taxes	0	0
Debt reacquisition costs	0	0
Deferred capital project	0	19
Other	9	14
Total regulatory assets	129	133
Noncurrent Regulatory Assets [Member]
Regulatory Assets [Line Items]
Price risk management	161	121
Pension and other postretirement plans	239	247
Deferred income taxes	86	86
Debt reacquisition costs	16	15
Deferred capital project	0	0
Other	22	25
Total regulatory assets	$ 524	$ 494