Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 172	$ 174	$ 104
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	305	301	248
Increase (decrease) in net liabilities from price risk management activities	60	45	(18)
Regulatory deferrals—price risk management activities	(60)	(45)	18
Cascade Crossing transmission project	0	0	52
Deferred income taxes	40	39	11
Allowance for equity funds used during construction	(21)	(37)	(13)
Pension and other postretirement benefits	34	33	37
Regulatory deferral of settled derivative instruments	2	10	7
Unrealized losses on non-qualified benefit plan trust assets	6	7	3
Decoupling mechanism deferrals, net of amortization	14	6	(6)
Power cost deferrals, net of amortization	0	0	(6)
Other non-cash income and expenses, net	17	12	18
Changes in working capital, net of effects from purchase of 10% interest in Boardman in 2014:
(Increase) decrease in receivables and unbilled revenues	(11)	8	0
(Increase) decrease in margin deposits	(22)	(2)	37
Increase (decrease) in payables and accrued liabilities	6	(13)	14
Other working capital items, net	(4)	(12)	17
Increase (Decrease) in Customer Advances and Deposits	(1)	13	1
Proceeds received from Trojan spent fuel legal settlement	0	6	44
Contribution to non-qualified employee benefit trust	(9)	(8)	(6)
Contribution to voluntary employees’ benefit association trust	(4)	(3)	(3)
Other, net	(7)	(16)	(15)
Net cash provided by operating activities	517	518	544
Cash flows from investing activities:
Capital expenditures	(598)	(1,007)	(656)
Purchases of nuclear decommissioning trust securities	(19)	(19)	(26)
Sales of nuclear decommissioning trust securities	22	17	25
Distribution from (contribution to) nuclear decommissioning trust	50	(6)	(44)
Sales tax refund received - Tucannon River Wind Farm	23	0	0
Cash received in connection with purchase of 10% interest in Boardman, net of cash paid	0	8	0
Proceeds received from insurance recoveries	0	3	6
Proceeds from sale of properties	0	5	0
Other, net	0	5	3
Net cash used in investing activities	(522)	(994)	(692)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	145	585	380
Payments on long-term debt	(442)	0	(100)
Proceeds from issuance of common stock, net of issuance costs	271	0	67
Borrowings on short-term debt	0	0	35
Payments on short-term debt	0	0	(35)
Maturities of commercial paper, net			(17)
Issuance (maturities) of commercial paper, net	6	0
Dividends paid	(97)	(87)	(84)
Debt issuance costs	(1)	(2)	(3)
Net cash (used in) provided by financing activities	(118)	496	243
(Decrease) increase in cash and cash equivalents	(123)	20	95
Cash and cash equivalents, beginning of year	127	107	12
Cash and cash equivalents, end of year	4	127	107
Supplemental disclosures of cash flow information:
Cash paid for interest, net of amounts capitalized	108	86	90
Cash paid for income taxes	3	22	10
Non-cash investing and financing activities:
Accrued capital additions	32	70	84
Accrued dividends payable	28	23	22
Accrued sales tax refund related to Tucannon River Wind Farm	0	23	0
Preliminary engineering transferred to Construction work in progress from Other noncurrent assets	$ 0	$ 0	$ 9