Financial and Other Derivative Instruments (Netting Offsets of Derivative Assets and Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	$ 609	$ 694
Gross Amounts Offset in the Consolidated Statements of Financial Position	(437)	(447)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	172	247
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(505)	(605)
Gross Amounts Offset in the Consolidated Statements of Financial Position	402	430
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(103)	(175)
Natural gas
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	344	428
Gross Amounts Offset in the Consolidated Statements of Financial Position	(255)	(285)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	89	143
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(300)	(410)
Gross Amounts Offset in the Consolidated Statements of Financial Position	230	272
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(70)	(138)
Electricity
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	191	187
Gross Amounts Offset in the Consolidated Statements of Financial Position	(126)	(116)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	65	71
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(163)	(150)
Gross Amounts Offset in the Consolidated Statements of Financial Position	131	114
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(32)	(36)
Environmental & Other
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	74	58
Gross Amounts Offset in the Consolidated Statements of Financial Position	(56)	(46)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	18	12
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(41)	(44)
Gross Amounts Offset in the Consolidated Statements of Financial Position	41	44
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	0	0
Interest rate contracts
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	0	20
Gross Amounts Offset in the Consolidated Statements of Financial Position	0	0
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	0	20
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	0	0
Gross Amounts Offset in the Consolidated Statements of Financial Position	0	0
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	0	0
Foreign currency exchange contracts
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	0	1
Gross Amounts Offset in the Consolidated Statements of Financial Position	0	0
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	0	1
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(1)	(1)
Gross Amounts Offset in the Consolidated Statements of Financial Position	0	0
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	$ (1)	$ (1)