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Derivative Instruments and Hedging Activities - Volumetric Underlying Derivative Transactions (Details) $ in Millions |  | 9 Months Ended
--- | --- | ---
Dec. 31, 2019 USD ($) MWh MMBTU | Sep. 30, 2020 USD ($) MMBTU MWh
Natural Gas | Long |  |
Derivatives, Fair Value [Line Items] |  |
Derivative nonmonetary notional amount (energy measure) | MMBTU | 2 | 1
Power | Short |  |
Derivatives, Fair Value [Line Items] |  |
Derivative nonmonetary notional amount (energy measure) | MWh | 2 | 2
Interest | Long |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, notional amount | $ | $ 1,788 | $ 1,769

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- Definition Nominal or face amount used to calculate payment on derivative. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959 + Details
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