Fair Value Measurements - NPC - Level 3 (Details) - NPC - Commodity - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] | ||
| Beginning balance | $ (41) | $ (57) |
| Changes in fair value recognized in regulatory assets | (14) | (24) |
| Settlements | 4 | 8 |
| Ending balance | $ (51) | $ (73) |