Fair Value Measurements (Schedule of Valuation Process and Unobservable Inputs) (Details) - Power $ in Millions	Dec. 31, 2020 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2019 USD ($) $ / MWh $ / MMBTU
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets \| $	$ 5	$ 14
Derivative Liability \| $	$ (201)	$ (225)
Measurement Input, Commodity Forward Price \| Minimum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	23	22
Measurement Input, Commodity Forward Price \| Maximum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	37	34
Measurement Input, Commodity Forward Price \| Weighted Average \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	29	25
Measurement Input, Nodal Basis \| Minimum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	(6)	(6)
Measurement Input, Nodal Basis \| Maximum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0	0
Measurement Input, Nodal Basis \| Weighted Average \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	(2)	(2)
Measurement Input, Commodity Future Price \| Minimum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input \| $ / MMBTU	2	(1)
Measurement Input, Commodity Future Price \| Maximum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input \| $ / MMBTU	6	0
Measurement Input, Commodity Future Price \| Weighted Average \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input \| $ / MMBTU	3	0

Value of input used to measure net derivative asset (liability).

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-Publisher FASB
-Name Accounting Standards Codification
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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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