Fair Value (Unobservable Inputs Related to Level 3 Assets and Liabilities) (Details) $ in Millions	Mar. 31, 2026 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2025 USD ($) $ / MWh $ / MMBTU
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	$ 723	$ 707
Derivative Liabilities	(750)	(597)
Natural gas
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	289	372
Derivative Liabilities	(333)	(329)
Electricity
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	357	275
Derivative Liabilities	(370)	(235)
Level 3
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	119	153
Level 3 | Natural gas
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	99	109
Derivative Liabilities	$ (79)	$ (82)
Level 3 | Natural gas | Forward basis price | Minimum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(1.18)	(1.35)
Level 3 | Natural gas | Forward basis price | Maximum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	4.90	9.33
Level 3 | Natural gas | Forward basis price | Weighted Average | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(0.18)	(0.13)
Level 3 | Electricity
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	$ 16	$ 33
Derivative Liabilities	$ (109)	$ (52)
Level 3 | Electricity | Forward basis price | Minimum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(40.45)	(21.82)
Level 3 | Electricity | Forward basis price | Maximum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	20.40	17.79
Level 3 | Electricity | Forward basis price | Weighted Average | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(9.05)	(5.58)