v3.3.1.900

Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |
Current | $ 216 | $ 195 |
Non-current | 12 | 49 |
Total | $ 228 | 244 |
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract] |  |  |
Property, plant and equipment, salvage value (as a percent) | 10.00% |  |
Property, plant and equipment, salvage value of rotables (as a percent) | 0.15% |  |
Impairment losses | $ 0 | 123 | $ 16
Asset retirement obligations | $ 47 | 47 |
Freestone Energy Center [Member] |  |  |
Jointly Owned Plants [Abstract] |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share | 75.00% |  |
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service | $ 393 |  |
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation | (148) |  |
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress | $ 0 |  |
Hidalgo Energy Center [Member] |  |  |
Jointly Owned Plants [Abstract] |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share | 78.50% |  |
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service | $ 256 |  |
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation | (110) |  |
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress | 0 |  |
Debt Service |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |
Current | 28 | 10 |
Non-current | 8 | 25 |
Total | 36 | 35 |
Rent Reserve [Member] |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |
Current | 0 | 4 |
Non-current | 0 | 0 |
Total | 0 | 4 |
Construction Major Maintenance |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |
Current | 50 | 54 |
Non-current | 2 | 17 |
Total | 52 | 71 |
Security Project Insurance |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |
Current | 136 | 127 |
Non-current | 0 | 5 |
Total | 136 | 132 |
Other |  |  |
Restricted Cash and Cash Equivalents Items [Line Items] |  |  |
Current | 2 | 0 |
Non-current | 2 | 2 |
Total | $ 4 | $ 2 |
Greenfield [Member] |  |  |
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract] |  |  |
Ownership percentage in equity method investment | 50.00% |  |
Whitby [Member] |  |  |
Basis Of Presentation and Summary of Significant Accounting Policies (Textuals) [Abstract] |  |  |
Ownership percentage in equity method investment | 50.00% |  |

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