Derivatives - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) gal in Millions, certificate in Millions, T in Millions, MMBTU in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($) certificate GWh MMBTU T gal	Dec. 31, 2024 USD ($) certificate MMBTU GWh T gal
Natural gas
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount, energy measure | MMBTU	4,017	4,568
Electricity
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount, energy measure | GWh	881,426	796,982
Financial transmission rights / Congestion revenue rights
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount, energy measure | GWh	254,680	248,742
Coal
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount, mass | T	29	27
Fuel oil
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount, volume | gal	3	2
Emissions
Derivatives, Fair Value [Line Items]
Derivative, nonmonetary notional amount, mass | T	33	28
Renewable energy certificates
Derivatives, Fair Value [Line Items]
Nonmonetary notional volume | certificate	29	31
Interest rate swaps – variable/fixed
Derivatives, Fair Value [Line Items]
Derivative, notional amount | $	$ 5,716	$ 5,300
Interest rate swaps – fixed/variable
Derivatives, Fair Value [Line Items]
Derivative, notional amount | $	$ 700	$ 700