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Accounting for Derivative Instruments and Hedging Activities - Effect on the Company's of Accumulated OCI Balance Attributable to Cash Flow Hedge Derivatives, Net (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Derivative [Line Items] |  |  |
Beginning balance | $ (1,234) | $ 1,968 | $ 4,446
Reclassified from accumulated OCI to income: |  |  |
Sale of NRG Yield and Renewables |  | 25 | 0
Ending balance | 1,658 | (1,234) | 1,968
Interest rate contracts | AOCI Including Portion Attributable to Noncontrolling Interest |  |  |
Derivative [Line Items] |  |  |
Beginning balance | 0 | (54) | (66)
Reclassified from accumulated OCI to income: |  |  |
Ending balance |  | 0 | (54)
Interest rate contracts | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent |  |  |
Reclassified from accumulated OCI to income: |  |  |
Due to realization of previously deferred amounts | $ 8 |  | 12
Interest rate contracts | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent |  |  |
Reclassified from accumulated OCI to income: |  |  |
Mark-to-market of cash flow hedge accounting contracts |  | $ 21 | $ 0

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- Definition Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e689-108580 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580 + Details
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