Financial and Other Derivative Instruments (Netting Offsets of Derivative Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	$ 1,391	$ 567
Gross Amounts Offset in the Consolidated Statements of Financial Position	(1,120)	(411)
Derivative assets, net	271	156
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(1,508)	(533)
Gross Amounts Offset in the Consolidated Statements of Financial Position	1,078	405
Derivative liabilities, net	(430)	(128)
Natural gas
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	454	233
Gross Amounts Offset in the Consolidated Statements of Financial Position	(394)	(156)
Derivative assets, net	60	77
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(594)	(223)
Gross Amounts Offset in the Consolidated Statements of Financial Position	347	151
Derivative liabilities, net	(247)	(72)
Electricity
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	643	180
Gross Amounts Offset in the Consolidated Statements of Financial Position	(441)	(120)
Derivative assets, net	202	60
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(622)	(168)
Gross Amounts Offset in the Consolidated Statements of Financial Position	443	125
Derivative liabilities, net	(179)	(43)
Environmental & Other
Derivative assets
Gross Amounts of Recognized Assets (Liabilities)	294	154
Gross Amounts Offset in the Consolidated Statements of Financial Position	(285)	(135)
Derivative assets, net	9	19
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(288)	(137)
Gross Amounts Offset in the Consolidated Statements of Financial Position	288	129
Derivative liabilities, net	0	(8)
Foreign currency exchange contracts
Derivative liabilities
Gross Amounts of Recognized Assets (Liabilities)	(4)	(5)
Gross Amounts Offset in the Consolidated Statements of Financial Position	0	0
Derivative liabilities, net	$ (4)	$ (5)