Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) $ in Millions	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mark-to-market derivatives—Economic hedges	$ 22,159	$ 12,393
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mark-to-market derivatives—Economic hedges	8,994	3,830
Cash collateral received	479	372
Economic Hedges \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Mark-to-market derivatives—Economic hedges	$ 1,694	$ (232)
Economic Hedges \| Level 3 \| Minimum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Forward power price (Non-congestion)	2.43	4.77
Forward power price (Congestion)	1.61	3.14
Forward gas price	(2.93)	(0.46)
Economic Hedges \| Level 3 \| Minimum \| Option Model
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Volatility percentage	0.10	0.14
Economic Hedges \| Level 3 \| Maximum \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Forward power price (Non-congestion)	181	154
Forward power price (Congestion)	180	154
Forward gas price	21	15
Economic Hedges \| Level 3 \| Maximum \| Option Model
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Volatility percentage	1.10	1.97
Economic Hedges \| Level 3 \| Average \| Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Forward power price (Non-congestion)	49	54
Forward power price (Congestion)	52	50
Forward gas price	3.20	3.52
Economic Hedges \| Level 3 \| Average \| Option Model
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Volatility percentage	0.57	0.59