Derivative Instruments (Significant Unobservable Inputs) (Details) - Level 3	9 Months Ended
	Sep. 30, 2025 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	$ 1,891,000,000
Financial and Nonfinancial Liabilities, Fair Value Disclosure	986,000,000
Forward Contracts - Power [Member] | Forward Contracts - Power [Member] | Forward Price [Member] | Maximum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	199
Forward Contracts - Power [Member] | Forward Contracts - Power [Member] | Forward Price [Member] | Minimum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	(4)
Forward Contracts - Power [Member] | Forward Contracts - Power [Member] | Forward Price [Member] | Weighted Average [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	54
Forward Contracts - Power [Member] | Derivative Financial Instruments, Assets [Member] | Forward Contracts - Power [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	496,000,000
Forward contracts - Gas [Member] | Forward contracts - Gas [Member] | Forward Price [Member] | Maximum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	13
Forward contracts - Gas [Member] | Forward contracts - Gas [Member] | Forward Price [Member] | Minimum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	(2)
Forward contracts - Gas [Member] | Forward contracts - Gas [Member] | Forward Price [Member] | Weighted Average [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	4
Forward contracts - Gas [Member] | Derivative Financial Instruments, Assets [Member] | Forward contracts - Gas [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	396,000,000
Forward contracts - Congestion [Member] | Forward contracts - Congestion [Member] | Forward Price [Member] | Maximum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	36
Forward contracts - Congestion [Member] | Forward contracts - Congestion [Member] | Forward Price [Member] | Minimum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	(76)
Forward contracts - Congestion [Member] | Forward contracts - Congestion [Member] | Forward Price [Member] | Weighted Average [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	0
Forward contracts - Congestion [Member] | Derivative Financial Instruments, Assets [Member] | Forward contracts - Congestion [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	$ 41,000,000
Option Contracts, Power [Member] | Option Contracts, Power [Member] | Implied Correlations [Member] | Maximum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	75.00%
Option Contracts, Power [Member] | Option Contracts, Power [Member] | Implied Correlations [Member] | Minimum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	70.00%
Option Contracts, Power [Member] | Option Contracts, Power [Member] | Implied Correlations [Member] | Weighted Average [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	72.00%
Option Contracts, Power [Member] | Option Contracts, Power [Member] | Implied Volatilities [Member] | Maximum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	202.00%
Option Contracts, Power [Member] | Option Contracts, Power [Member] | Implied Volatilities [Member] | Minimum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	37.00%
Option Contracts, Power [Member] | Option Contracts, Power [Member] | Implied Volatilities [Member] | Weighted Average [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	78.00%
Option Contracts, Power [Member] | Derivative Financial Instruments, Assets [Member] | Option Contracts, Power [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	$ 21,000,000
Option Contracts, Primarily Gas [Member] | Option Contracts, Gas [Member] | Implied Correlations [Member] | Maximum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	100.00%
Option Contracts, Primarily Gas [Member] | Option Contracts, Gas [Member] | Implied Correlations [Member] | Minimum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	70.00%
Option Contracts, Primarily Gas [Member] | Option Contracts, Gas [Member] | Implied Correlations [Member] | Weighted Average [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	93.00%
Option Contracts, Primarily Gas [Member] | Option Contracts, Gas [Member] | Implied Volatilities [Member] | Maximum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	145.00%
Option Contracts, Primarily Gas [Member] | Option Contracts, Gas [Member] | Implied Volatilities [Member] | Minimum | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	16.00%
Option Contracts, Primarily Gas [Member] | Option Contracts, Gas [Member] | Implied Volatilities [Member] | Weighted Average [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	49.00%
Option Contracts, Primarily Gas [Member] | Derivative Financial Instruments, Assets [Member] | Option Contracts, Gas [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	$ 85,000,000
Full Requirements and Unit Contingent Contracts [Member] | Full Requirements and Unit Contingent Contracts [Member] | Forward Price [Member] | Maximum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	426
Full Requirements and Unit Contingent Contracts [Member] | Full Requirements and Unit Contingent Contracts [Member] | Forward Price [Member] | Minimum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	19
Full Requirements and Unit Contingent Contracts [Member] | Full Requirements and Unit Contingent Contracts [Member] | Forward Price [Member] | Weighted Average [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward price (in dollars per energy unit)	$ 83
Full Requirements and Unit Contingent Contracts [Member] | Full Requirements and Unit Contingent Contracts [Member] | Customer Migration Rate [Member] | Maximum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	14.00%
Full Requirements and Unit Contingent Contracts [Member] | Full Requirements and Unit Contingent Contracts [Member] | Customer Migration Rate [Member] | Minimum | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	0.00%
Full Requirements and Unit Contingent Contracts [Member] | Full Requirements and Unit Contingent Contracts [Member] | Customer Migration Rate [Member] | Weighted Average [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Inputs, Expected Rates	1.00%
Full Requirements and Unit Contingent Contracts [Member] | Derivative Financial Instruments, Assets [Member] | Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	$ 356,000,000
Forward contracts - Other [Member] [Member] | Derivative Financial Instruments, Assets [Member] | Forward contracts - Other [Member] [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets, Fair Value Disclosure	496,000,000
Derivative Financial Instruments, Liabilities [Member] | Forward Contracts - Power [Member] | Forward Contracts - Power [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	404,000,000
Derivative Financial Instruments, Liabilities [Member] | Forward contracts - Gas [Member] | Forward contracts - Gas [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	101,000,000
Derivative Financial Instruments, Liabilities [Member] | Forward contracts - Congestion [Member] | Forward contracts - Congestion [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	21,000,000
Derivative Financial Instruments, Liabilities [Member] | Option Contracts, Power [Member] | Option Contracts, Power [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	1,000,000
Derivative Financial Instruments, Liabilities [Member] | Option Contracts, Primarily Gas [Member] | Option Contracts, Gas [Member] | Option Models [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	104,000,000
Derivative Financial Instruments, Liabilities [Member] | Full Requirements and Unit Contingent Contracts [Member] | Full Requirements and Unit Contingent Contracts [Member] | Discounted Cash Flow Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	172,000,000
Derivative Financial Instruments, Liabilities [Member] | Forward contracts - Other [Member] [Member] | Forward contracts - Other [Member] [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 183,000,000