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Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2016
Property, Plant and Equipment [Line Items] |  |  |  |
Unamortized Debt Issuance Expense | $ 11 | $ 11 |  |
Other Investments | $ 1 | 0 |  |
Business days after the invoice date | 16 |  |  |
Days after the due date | 45 |  |  |
Wholesale accounts receivable written off | $ 0 | 0 | $ 0 |
Margin deposit | 8 | 33 |  |
Letters of Credit Outstanding, Amount | $ 17 | $ 63 |  |
Public Utilities, Allowance for Funds Used During Construction, Rate | 7.30% | 7.30% | 7.40% |
Public Utilities, Allowance for Funds Used During Construction, Capitalized Interest | $ 11 | $ 13 | $ 22 |
Allowance for equity funds used during construction | 21 | 21 | $ 37 |
Construction in Progress, Gross | 634 |  |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | $ 213 | $ 545 |  |
Depreciation expense rate | 3.50% | 3.60% | 3.60% |
Finite-Lived Intangible Assets, Accumulated Amortization | $ 257 | $ 227 |  |
Amortization of Intangible Assets | 44 | $ 38 | $ 25 |
Future Amortization Expense, Year One | 45 |  |  |
Future Amortization Expense, Year Two | 44 |  |  |
Future Amortization Expense, Year Three | 38 |  |  |
Future Amortization Expense, Year Four | 34 |  |  |
Future Amortization Expense, Year Five | 22 |  |  |
Power Cost Deadband - Lower Threshold | 15 |  |  |
Power Cost Deadband - Upper Threshold | $ 30 |  |  |
Public Utilities, Approved Return on Equity, Percentage | 9.60% | 9.68% | 9.75% |
Franchise taxes | $ 43 | $ 43 | $ 42 |
Deferred Tax Assets, Regulatory Assets and Liabilities | 29 | 42 |  |
Public Utilities, Property, Plant and Equipment, Amount of Construction Work in Process Included in Rate Base |  |  |  | $ 514
excess tax benefits recognized related to share-based payment awards | 1 |  |  |
Proceeds and Excess Tax Benefit from Share-based Compensation | 3 | 2 |  |
Type of Arrangement [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Public Utilities, Property, Plant and Equipment, Construction Work in Progress | 514 |  |  |
Noncurrent Regulatory Assets [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Deferred Tax Assets, Regulatory Assets and Liabilities | 86 | 86 |  |
Noncurrent Regulatory Liabilities [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
Asset Retirement Obligations, Noncurrent | $ 49 | $ 45 |  |

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