Financial and Other Derivative Instruments (Netting Offsets of Derivative Assets and Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	$ 861	$ 1,197
Gross Amounts Offset in the Consolidated Statements of Financial Position	(582)	(791)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	279	406
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(832)	(1,172)
Gross Amounts Offset in the Consolidated Statements of Financial Position	585	863
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(247)	(309)
Natural gas
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	421	637
Gross Amounts Offset in the Consolidated Statements of Financial Position	(275)	(416)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	146	221
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(412)	(615)
Gross Amounts Offset in the Consolidated Statements of Financial Position	277	429
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(135)	(186)
Electricity
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	255	421
Gross Amounts Offset in the Consolidated Statements of Financial Position	(157)	(243)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	98	178
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(251)	(388)
Gross Amounts Offset in the Consolidated Statements of Financial Position	158	297
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(93)	(91)
Environmental & Other
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	178	139
Gross Amounts Offset in the Consolidated Statements of Financial Position	(150)	(132)
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	28	7
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(168)	(150)
Gross Amounts Offset in the Consolidated Statements of Financial Position	150	137
Net Amounts of Assets (Liabilities) Presented in the Consolidated Statements of Financial Position	(18)	(13)
Interest rate contracts
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	6	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	6	0
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	0	(16)
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	(16)
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)	(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	$ (1)	$ (3)