Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 193	$ 172	$ 174
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	321	305	301
Deferred income taxes	37	40	39
Allowance for equity funds used during construction	(21)	(21)	(37)
Pension and other postretirement benefits	28	34	33
Regulatory deferral of settled derivative instruments	2	2	10
Unrealized losses on non-qualified benefit plan trust assets	5	6	7
Decoupling mechanism deferrals, net of amortization	(6)	14	6
Other non-cash income and expenses, net	5	20	14
Changes in working capital:
(Increase) decrease in receivables and unbilled revenues	(9)	(11)	8
Decrease (increase) in margin deposits	25	(22)	(2)
Increase (decrease) in payables and accrued liabilities	15	6	(13)
Other working capital items, net	(4)	(4)	(12)
Cash received to be returned to customers pursuant to the Residential Exchange Program, net of amortization	(6)	(1)	13
Contribution to non-qualified employee benefit trust	(10)	(9)	(8)
Contribution to voluntary employees’ benefit association trust	(2)	(4)	(3)
Other, net	(20)	(7)	(10)
Net cash provided by operating activities	553	520	520
Cash flows from investing activities:
Capital expenditures	(584)	(598)	(1,007)
Purchases of nuclear decommissioning trust securities	(25)	(19)	(19)
Sales of nuclear decommissioning trust securities	27	22	17
Distribution from (contribution to) nuclear decommissioning trust	0	50	(6)
Sales tax refund received - Tucannon River Wind Farm	0	23	0
Cash received in connection with purchase of 10% interest in Boardman, net of cash paid	0	0	8
Other, net	(3)	0	13
Net cash used in investing activities	(585)	(522)	(994)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	290	145	585
Payments on long-term debt	(133)	(442)	0
Proceeds from issuance of common stock, net of issuance costs	0	271	0
(Maturities) issuances of commercial paper, net	(6)	6	0
Dividends paid	(110)	(97)	(87)
Other	(7)	(4)	(4)
Net cash provided by (used in) financing activities	34	(121)	494
Increase (decrease) in cash and cash equivalents	2	(123)	20
Cash and cash equivalents, beginning of year	4	127	107
Cash and cash equivalents, end of year	6	4	127
Supplemental disclosures of cash flow information:
Cash paid for interest, net of amounts capitalized	104	108	86
Cash paid for income taxes	16	3	22
Non-cash investing and financing activities:
Accrued capital additions	50	32	70
Accrued dividends payable	30	28	23
Accrued sales tax refund related to Tucannon River Wind Farm	0	0	23
Assets obtained under leasing arrangements	$ 78	$ 0	$ 0