Fair Value of Financial Assets and Liabilities - Fair Value Assets and Liabilities Measure on a Recurring Basis Gain Loss Included in Earnings (Details) - Level 3 - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Total (losses) gains included in net income	$ 95	$ (185)	$ (35)	$ (491)
Total unrealized (losses) gains	207	(4)	112	25
Operating revenues
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Total (losses) gains included in net income	(37)	(103)	1	(275)
Total unrealized (losses) gains	74	113	66	261
Purchased power and fuel
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Total (losses) gains included in net income	131	(82)	(38)	(218)
Total unrealized (losses) gains	132	(117)	44	(236)
Other, net
Fair Value Assets and Liabilities Measured on a Recurring Basis Gain Loss Included in Earnings [Line Items]
Total (losses) gains included in net income	1	0	2	0
Total unrealized (losses) gains	$ 1	$ 0	$ 2	$ 0