Financial and Other Derivative Instruments (Netting Offsets of Derivative Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	$ 2,377	$ 1,391
Gross Amounts Offset in the Consolidated Statements of Financial Position	(1,911)	(1,120)
Derivative assets, net	466	271
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(2,562)	(1,508)
Gross Amounts Offset in the Consolidated Statements of Financial Position	1,829	1,078
Derivative liabilities, net	(733)	(430)
Natural gas
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	711	454
Gross Amounts Offset in the Consolidated Statements of Financial Position	(679)	(394)
Derivative assets, net	32	60
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(905)	(594)
Gross Amounts Offset in the Consolidated Statements of Financial Position	553	347
Derivative liabilities, net	(352)	(247)
Electricity
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	1,334	643
Gross Amounts Offset in the Consolidated Statements of Financial Position	(905)	(441)
Derivative assets, net	429	202
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(1,325)	(622)
Gross Amounts Offset in the Consolidated Statements of Financial Position	950	443
Derivative liabilities, net	(375)	(179)
Environmental & Other
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	332	294
Gross Amounts Offset in the Consolidated Statements of Financial Position	(327)	(285)
Derivative assets, net	5	9
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(326)	(288)
Gross Amounts Offset in the Consolidated Statements of Financial Position	326	288
Derivative liabilities, net	0	0
Foreign currency exchange contracts
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(6)	(4)
Gross Amounts Offset in the Consolidated Statements of Financial Position	0	0
Derivative liabilities, net	$ (6)	$ (4)