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Derivatives Instruments (Notional Volumes of Commodity Swaps and Forward Contracts Designated for Regulatory Deferral) (Details) - Regulatory deferral - Commodity swaps and forwards - Purchases bbl in Millions, T in Millions, MWh in Millions, MMBTU in Millions	12 Months Ended
	Dec. 31, 2019 MMBTU MWh T bbl
Coal | 2020
Derivative [Line Items]
Coal (metric tonnes) | T	0
Coal | 2021-2022
Derivative [Line Items]
Coal (metric tonnes) | T	1
Natural gas | 2020
Derivative [Line Items]
Natural Gas (Mmbtu) / Power (MWh) | MMBTU	12
Natural gas | 2021-2022
Derivative [Line Items]
Natural Gas (Mmbtu) / Power (MWh) | MMBTU	21
Heavy fuel oil | 2020
Derivative [Line Items]
Heavy fuel oil (bbls) | bbl	0
Heavy fuel oil | 2021-2022
Derivative [Line Items]
Heavy fuel oil (bbls) | bbl	1
Power | 2020
Derivative [Line Items]
Natural Gas (Mmbtu) / Power (MWh) | MWh	1
Power | 2021-2022
Derivative [Line Items]
Natural Gas (Mmbtu) / Power (MWh) | MWh	3

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- Definition

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- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

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- Definition

Nominal mass used to calculate payments on a derivative instrument.

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- Definition

Nominal volume used to calculate payments on a derivative instrument.

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