Fair Value (Unobservable Inputs related to Level 3 Assets and Liabilities) (Details) $ in Millions	Mar. 31, 2024 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2023 USD ($) $ / MMBTU $ / MWh
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	$ 891	$ 1,197
Derivative Liabilities	(935)	(1,172)
Natural gas
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	499	637
Derivative Liabilities	(506)	(615)
Electricity
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	235	421
Derivative Liabilities	$ (267)	$ (388)
Level 3 | Natural gas | Forward basis price | Minimum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(1.27)	(1.57)
Level 3 | Natural gas | Forward basis price | Maximum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	2.42	6.27
Level 3 | Natural gas | Forward basis price | Weighted Average | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(0.09)	(0.08)
Level 3 | Electricity | Forward basis price | Minimum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(18.83)	(18.49)
Level 3 | Electricity | Forward basis price | Maximum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	11.90	15.47
Level 3 | Electricity | Forward basis price | Weighted Average | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(4.53)	(3.99)
Recurring | Level 3
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	$ 200	$ 350
Recurring | Level 3 | Natural gas
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	119	179
Derivative Liabilities	(122)	(157)
Recurring | Level 3 | Electricity
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	77	163
Derivative Liabilities	$ (102)	$ (116)