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Summary of Significant Accounting Policies - Additional (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Funds Deposited by Counterparties |  |  |
Number of months beyond which company can not predict the holding of collateral (in months) | 12 months |  |
Collateral received from GenOn |  |  | $ 79
Accounts Receivable, Net [Abstract] |  |  |
Allowance for doubtful accounts | $ 32 | $ 28 |
Project Development Costs and Capitalized Interest |  |  |
Amount of interest capitalized | 7 | 20 | 29
Finite-Lived Intangible Assets, Net [Abstract] |  |  |
Intangible assets, accumulated amortization | $ 1,151 | 1,573 |
Income Taxes |  |  |
Unrecognized tax benefits, more-likely-than-not threshold percentage | 50.00% |  |
Lease Revenue |  |  |
Lease, term of contract | 20 years |  |
Lessor Accounting |  |  |
Contingent rental income | $ 104 | 253 | 272
Gross Receipts and Sales Taxes |  |  |
Gross Receipts Tax | 99 | 92 | 101
Cost of Energy for Retail Operations |  |  |
Transmission and distribution charges not yet billed | 105 | 107 | 90
Foreign Currency Translation and Transaction Gains and Losses |  |  |
Cumulative translation adjustment | (13) | (2) | (11)
Marketing and Advertising Expense |  |  |
Advertising expense | 73 | 66 | $ 79
Reorganization Costs |  |  |
Severance costs | $ 90 | $ 44 |
South Texas Project |  |  |
Property, Plant and Equipment |  |  |
Ownership Interest (as a percent) | 44.00% |  |

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