Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Cash Flow from Operating Activities:
Net Income	$ 120	$ 102	$ 359	$ 314
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	206	213	403	418
Accretion expenses			5	4
Regulatory assets/liabilities amortization			28	83
Regulatory assets/liabilities carrying cost			11	13
Pension cost			56	66
Stock-based compensation			4
Earnings from equity method investments	(1)		(3)	(2)
Amortization of debt cost (premium)			(2)	(15)
Gain on disposal of property and equity method investment			(1)	(34)
Unrealized (gain) loss on marked-to-market derivative contracts			(18)	23
Deferred taxes			142	244
Other non-cash items			(30)	(2)
Changes in operating assets and liabilities:
Accounts receivable and unbilled revenues			143	85
Inventories			(14)	65
Other assets/liabilities			(22)	(108)
Cash distribution from equity method investments			7	6
Accounts payable and accrued liabilities			(168)	(12)
Taxes accrued			4	(7)
Regulatory assets/liabilities			21	(235)
Net Cash Provided by Operating Activities			925	906
Cash Flow from Investing Activities:
Capital expenditures			(1,069)	(674)
Contributions in aid of construction			21	41
Proceeds from sale of property, plant and equipment			3	43
Proceeds from sale of equity method and other investment			5	57
Receipts from affiliates				2
Cash distribution from equity method investments			2	2
Other investments and equity method investments, net			(7)	(8)
Net Cash Used in Investing Activities			(1,045)	(537)
Cash Flow from Financing Activities:
Non-current note issuance			294
Repayments of non-current debt			(23)	(45)
Receipts (repayments) of other short-term debt, net			158	(160)
Payments on tax equity financing arrangements			(60)	(53)
Repayments of capital leases			(31)	(4)
Repurchase of common stock			(3)	(4)
Issuance of common stock			(1)	(2)
Dividends paid			(268)	(134)
Net Cash Provided by (Used in) Financing Activities			66	(402)
Net Decrease in Cash, Cash Equivalents and Restricted Cash			(54)	(33)
Cash, Cash Equivalents and Restricted Cash, Beginning of Period			96	434	$ 434
Cash, Cash Equivalents and Restricted Cash, End of Period	$ 42	$ 401	42	401	$ 96
Supplemental Cash Flow Information
Cash paid for interest, net of amounts capitalized			99	114
Cash paid for income taxes			$ 8	$ 7