Financial and Other Derivative Instruments (Netting Offsets of Derivative Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	$ 723	$ 707
Gross Amounts Offset in the Consolidated Statements of Financial Position	(519)	(475)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	204	232
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(750)	(597)
Gross Amounts Offset in the Consolidated Statements of Financial Position	545	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)	289	372
Gross Amounts Offset in the Consolidated Statements of Financial Position	(170)	(235)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	119	137
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(333)	(329)
Gross Amounts Offset in the Consolidated Statements of Financial Position	210	227
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(123)	(102)
Electricity
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	357	275
Gross Amounts Offset in the Consolidated Statements of Financial Position	(285)	(194)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	72	81
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(370)	(235)
Gross Amounts Offset in the Consolidated Statements of Financial Position	280	186
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(90)	(49)
Environmental & Other
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	68	57
Gross Amounts Offset in the Consolidated Statements of Financial Position	(64)	(46)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	4	11
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(46)	(32)
Gross Amounts Offset in the Consolidated Statements of Financial Position	55	32
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	9	0
Interest rate contracts
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	8	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	8	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)