Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Cash Flow from Operating Activities:
Net Income	$ 100	$ 109	$ 459	$ 423
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	205	203	608	621
Accretion expenses			8	7
Regulatory assets/liabilities amortization			38	129
Regulatory assets/liabilities carrying cost			12	12
Pension cost			84	104
Stock-based compensation			5	1
Earnings from equity method investments		(2)	(3)	(4)
Amortization of debt premium			(3)	(17)
Gain on disposal of property and equity method investment			(1)	(33)
Unrealized gain on marked-to-market derivative contracts			(13)	(4)
Deferred taxes			166	329
Other non-cash items			(47)	(20)
Changes in operating assets and liabilities:
Accounts receivable and unbilled revenues			179	72
Inventories			(33)	59
Other assets/liabilities			(96)	(337)
Cash distribution from equity method investments			11	10
Accounts payable and accrued liabilities			(105)	52
Taxes accrued			10	11
Regulatory assets/liabilities			43	(201)
Net Cash Provided by Operating Activities			1,322	1,214
Cash Flow from Investing Activities:
Capital expenditures			(1,704)	(1,036)
Contributions in aid of construction			31	55
Proceeds from sale of property, plant and equipment			9	50
Proceeds from sale of equity method and other investment				57
Receipts from affiliates				6
Cash distribution from equity method investments			4	4
Other investments and equity method investments, net			(7)	(1)
Net Cash Used in Investing Activities			(1,667)	(865)
Cash Flow from Financing Activities:
Non-current note issuance			294
Repayments of non-current debt			(65)	(83)
Receipts (repayments) of other short-term debt, net			570	(159)
Payments on tax equity financing arrangements			(84)	(75)
Repayments of capital leases			(32)	(6)
Repurchase of common stock			(3)	(4)
Issuance of common stock			(1)	(2)
Transaction with noncontrolling interests			5
Dividends paid			(401)	(267)
Net Cash Provided by (Used in) Financing Activities			283	(596)
Net Decrease in Cash, Cash Equivalents and Restricted Cash			(62)	(247)
Cash, Cash Equivalents and Restricted Cash, Beginning of Period			96	434	$ 434
Cash, Cash Equivalents and Restricted Cash, End of Period	$ 34	$ 187	34	187	$ 96
Supplemental Cash Flow Information
Cash paid for interest, net of amounts capitalized			144	182
Cash paid for income taxes			$ 9	$ 9