Financial and Other Derivative Instruments (Netting Offsets of Derivative Assets and Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	$ 1,056	$ 707
Gross Amounts Offset in the Consolidated Statements of Financial Position	(748)	(475)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	308	232
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(962)	(597)
Gross Amounts Offset in the Consolidated Statements of Financial Position	757	445
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(205)	(152)
Natural gas
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	346	372
Gross Amounts Offset in the Consolidated Statements of Financial Position	(245)	(235)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	101	137
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(366)	(329)
Gross Amounts Offset in the Consolidated Statements of Financial Position	245	227
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(121)	(102)
Electricity
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	593	275
Gross Amounts Offset in the Consolidated Statements of Financial Position	(466)	(194)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	127	81
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(560)	(235)
Gross Amounts Offset in the Consolidated Statements of Financial Position	475	186
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(85)	(49)
Environmental & Other
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	73	57
Gross Amounts Offset in the Consolidated Statements of Financial Position	(37)	(46)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	36	11
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(35)	(32)
Gross Amounts Offset in the Consolidated Statements of Financial Position	37	32
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	2	0
Interest rate contracts
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	43	3
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	43	3
Foreign currency exchange contracts
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	1	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	1	0
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)