Fair Value (Unobservable Inputs Related to Level 3 Assets and Liabilities) (Details) $ in Millions	Sep. 30, 2026 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2025 USD ($) $ / MWh $ / MMBTU
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	$ 1,056	$ 707
Derivative Liabilities	(962)	(597)
Natural gas
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	346	372
Derivative Liabilities	(366)	(329)
Electricity
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	593	275
Derivative Liabilities	(560)	(235)
Level 3
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	145	153
Level 3 | Natural gas
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	86	109
Derivative Liabilities	$ (68)	$ (82)
Level 3 | Natural gas | Forward basis price | Minimum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(1.54)	(1.35)
Level 3 | Natural gas | Forward basis price | Maximum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	4.82	9.33
Level 3 | Natural gas | Forward basis price | Weighted Average | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MMBTU	(0.14)	(0.13)
Level 3 | Electricity
Unobservable Inputs Valuation Techniques [Line Items]
Derivative Assets	$ 29	$ 33
Derivative Liabilities	$ (149)	$ (52)
Level 3 | Electricity | Forward basis price | Minimum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(56.15)	(21.82)
Level 3 | Electricity | Forward basis price | Maximum | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	38.50	17.79
Level 3 | Electricity | Forward basis price | Weighted Average | Discounted Cash Flow
Unobservable Inputs Valuation Techniques [Line Items]
Forward basis price | $ / MWh	(19.04)	(5.58)