Balance Sheet Components Other Current Assets (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Other Current Assets [Line Items]
Prepaid expenses	$ 24	$ 39
Current deferred income tax asset	39	33
Margin deposits	20	11
Accrued sales tax refund related to Tucannon River Wind Farm	0	23
Assets from price risk management activities	7	6
Other	2	3
Other current assets	$ 92	$ 115