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Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Property, Plant and Equipment [Line Items] |  |  |
Regulatory Liabilities | $ 1,391 | $ 1,319 |
Capital Lease Obligations Incurred | 50 | (5) | $ (2)
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price | 3 | 0 | 0
Total Revenues | $ 1,991 | 2,009 | 1,923
Business days after the invoice date | 8 |  |
Other Investments | $ 112 | 30 |
Days after the due date | 45 |  |
Wholesale accounts receivable written off | $ 0 | 0 | $ 0
Margin deposit | 16 | 11 |
Letters of Credit Outstanding, Amount | $ 48 | $ 31 |
Public Utilities, Allowance for Funds Used During Construction, Rate | 7.30% | 7.30% | 7.30%
Public Utilities, Allowance for Funds Used During Construction, Capitalized Interest | $ 6 | $ 6 | $ 11
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity | $ 11 | $ 12 | $ 21
Depreciation expense rate | 3.60% | 3.60% | 3.50%
Finite-Lived Intangible Assets, Accumulated Amortization | $ 302 | $ 296 |
Amortization of Intangible Assets | 59 | $ 46 | $ 44
Future Amortization Expense, Year One | 60 |  |
Future Amortization Expense, Year Two | 52 |  |
Future Amortization Expense, Year Three | 44 |  |
Future Amortization Expense, Year Four | 38 |  |
Future Amortization Expense, Year Five | 29 |  |
Power Cost Deadband - Lower Threshold | 15 |  |
Power Cost Deadband - Upper Threshold | $ 30 |  |
Public Utilities, Approved Return on Equity, Percentage | 9.50% | 9.60% | 9.60%
Regulatory Liability, Noncurrent | $ 1,355 | $ 1,288 |
Franchise taxes | 45 | 43 | $ 43
Regulatory Assets, Noncurrent | 401 | 438 |
Pension and Other Postretirement Benefits Cost (Reversal of Cost) | 30 | 24 | 28
Proceeds from (Payments for) Other Financing Activities | (5) | (7) | (16)
Land, Buildings and Improvements [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 131 |  |
Pension and Other Postretirement Plans Costs [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory Assets | 3 |  |
Environmental Restoration Costs [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory Assets, Noncurrent | 25 |  |
Asset Retirement Obligation Costs [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory Liabilities | 53 | 52 |
Deferred Income Tax Charge [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory Liabilities | 267 | 277 |
Environmental Restoration Costs [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Regulatory Liabilities | 1 | 3 |
Regulatory Liability, Noncurrent |  | 3 |
Minimum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Finance Lease, Right-of-Use Asset | 40 |  |
Maximum [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Finance Lease, Right-of-Use Asset | 50 |  |
Debt [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Proceeds from (Payments for) Other Financing Activities |  |  | 9
Restatement Adjustment [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Pension and Other Postretirement Benefits Cost (Reversal of Cost) | $ 5 | $ 4 | $ 7

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