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Balance Sheet Components (Details) - USD ($) |  | 3 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 09, 2016 | Sep. 30, 2016 | Mar. 31, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015 | May 04, 2016 | Jan. 31, 2016 | Jan. 11, 2016 | Jan. 08, 2016 | Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Finite-Lived Intangible Assets, Accumulated Amortization |  | $ 260,000,000 |  |  | $ 260,000,000 |  |  |  |  |  | $ 227,000,000
Amortization of Intangible Assets |  | 11,000,000 |  | $ 10,000,000 | 33,000,000 | $ 28,000,000 |  |  |  |  |
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment |  | 615,000,000 |  |  | 615,000,000 |  |  |  |  |  | 424,000,000
Phase-in Plan, Amount of Costs Deferred for Rate-making Purposes |  | 514,000,000 |  |  | 514,000,000 |  |  |  |  |  |
Capital Leased Assets, Gross |  | 57,000,000 |  |  | 57,000,000 |  |  |  |  |  |
Amortization of Leased Asset |  | 1,000,000 |  |  | 2,000,000 |  |  |  |  |  |
Capital Leases, Income Statement, Interest Expense |  | 1,000,000 |  |  | 3,000,000 |  |  |  |  |  |
Capital Leases, Future Minimum Payments, Remainder of Fiscal Year |  | 2,000,000 |  |  | 2,000,000 |  |  |  |  |  |
Syndicated credit facility scheduled to expire in 2019 |  | $ 500,000,000 |  |  | $ 500,000,000 |  |  |  |  |  |
Debt Instrument, Covenant Description |  |  |  |  | 0.65 |  |  |  |  |  |
Ratio of Indebtedness to Net Capital |  | 0.510 |  |  | 0.510 |  |  |  |  |  |
Short-term debt |  | $ 0 |  |  | $ 0 |  |  |  |  |  | $ 6,000,000
Line of Credit Facility, Remaining Borrowing Capacity |  | 500,000,000 |  |  | 500,000,000 |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | 160,000,000 |  |  | 160,000,000 |  |  |  |  |  |
Letters of credit issued |  | 73,000,000 |  |  | 73,000,000 |  |  |  |  |  |
Authorized Short-Term Debt |  | $ 900,000,000 |  |  | $ 900,000,000 |  |  |  |  |  |
Debt Instrument, Redemption, Description |  | 25 |  |  | 200 |  |  |  |  |  |
Proceeds from Issuance of Long-term Debt |  | $ 75,000,000 |  |  | $ 75,000,000 |  | $ 50,000,000 |  |  | $ 140,000,000 |
Unsecured term bank loan rate - minimum |  | 1.20% |  |  | 1.20% |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  | 3.81% | 5.80% | 2.51% |
Extinguishment of Debt, Amount |  |  | $ 133,000,000 |  | $ 133,000,000 | $ 442,000,000 |  |  |  |  |
Notes Payable to Banks [Member] |  |  |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Extinguishment of Debt, Amount | $ 75,000,000 |  |  |  |  |  |  |  |  |  |
Long-term Debt [Member] |  |  |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |
Extinguishment of Debt, Amount | $ 58,000,000 |  |  |  |  |  |  |  |  |  |

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- Definition FERC-authorized short-term debt through February 6, 2012 + References No definition available. + Details
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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition The expense charged against earnings for the periodic recognition of capitalized leases. This element may apply to energy companies that lease mineral producing properties and to other enterprises that capitalize property, plant, or equipment obtained through capital leases. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45031-112735 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
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- Definition Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45014-112735 + Details
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- Definition Amount of minimum lease payments for capital leases due in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References No definition available. + Details
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- Definition The financing charge for leasing arrangements meeting the criteria for capitalization. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45031-112735 + Details
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- Definition Description of minimum financial levels (for example, tangible net worth and working capital) and achievement of certain financial ratios (for example, working capital ratio and debt service coverage ratio), and adherence to certain clauses which generally require or restrict certain actions (for example, entering into a debt arrangement with equal or greater seniority, and selling or discontinuing a certain business segment or material subsidiary) to be in compliance with the covenant clauses of the debt agreement. May also include a discussion of the adverse consequences that would result if the entity violates or fails to satisfy the covenants. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823 + Details
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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Description of debt redemption features under terms of the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph e -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823 + Details
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- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for letter of credit arrangements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (b)(1)(i) -URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729 + Details
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- Definition Discloses the amount of construction work in process that is included in the rate making process at period end. + References No definition available. + Details
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- Definition Period end book value of other property, plant and equipment (PPE) owned (but not classified elsewhere) by the public utility. + References No definition available. + Details
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