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Investments (Investments Under Equity Method of Accounting) (Parenthetical) (Detail) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
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Schedule of Equity Method Investments [Line Items] |  |  |
Liabilities, other deferred credits and other liabilities | $ 26,027 | $ 17,075 |
NedPower Mount Storm LLC |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |
Liabilities, other deferred credits and other liabilities |  | $ 1 | $ 17

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- Details
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