Acquisitions, Discontinued Operations and Dispositions -Fair Values of Derivatives Assets and Liabilities as of the Acquisition Closing Date (Details) - Direct Energy $ in Millions	Jan. 05, 2021 USD ($)
Derivative [Line Items]
Derivatives assets	$ 1,545
Derivatives liabilities	1,828
Quoted Prices in Active Markets for Identical Assets (Level 1)
Derivative [Line Items]
Derivatives assets	155
Derivatives liabilities	207
Significant Observable Inputs (Level 2)
Derivative [Line Items]
Derivatives assets	1,272
Derivatives liabilities	1,489
Level 3
Derivative [Line Items]
Derivatives assets	118
Derivatives liabilities	$ 132