Fair Value (Unobservable Inputs related to Level 3 Assets and Liabilities) (Details) $ in Millions	Dec. 31, 2021 USD ($) $ / MWh $ / MMBTU	Dec. 31, 2020 USD ($) $ / MMBTU $ / MWh
Unobservable Input Valuation Techniques [Line Items]
Derivative Assets	$ 1,391	$ 567
Derivative Liabilities	(1,508)	(533)
Natural Gas
Unobservable Input Valuation Techniques [Line Items]
Derivative Assets	454	233
Derivative Liabilities	(594)	(223)
Electricity
Unobservable Input Valuation Techniques [Line Items]
Derivative Assets	643	180
Derivative Liabilities	$ (622)	$ (168)
Level 3 | Discounted Cash Flow | Forward basis price | Natural Gas | Minimum
Unobservable Input Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(1.36)	(0.86)
Level 3 | Discounted Cash Flow | Forward basis price | Natural Gas | Maximum
Unobservable Input Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	3.82	2.50
Level 3 | Discounted Cash Flow | Forward basis price | Natural Gas | Weighted Average
Unobservable Input Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(0.04)	(0.07)
Level 3 | Discounted Cash Flow | Forward basis price | Electricity | Minimum
Unobservable Input Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(12)	(9)
Level 3 | Discounted Cash Flow | Forward basis price | Electricity | Maximum
Unobservable Input Valuation Techniques [Line Items]
Forward basis price | $ / MWh	7	6
Level 3 | Discounted Cash Flow | Forward basis price | Electricity | Weighted Average
Unobservable Input Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(2)	0
Recurring | Level 3
Unobservable Input Valuation Techniques [Line Items]
Derivative Assets	$ 218	$ 116
Derivative Liabilities	(433)	(118)
Recurring | Level 3 | Natural Gas
Unobservable Input Valuation Techniques [Line Items]
Derivative Assets	66	60
Derivative Liabilities	(245)	(76)
Recurring | Level 3 | Electricity
Unobservable Input Valuation Techniques [Line Items]
Derivative Assets	143	52
Derivative Liabilities	$ (188)	$ (42)