Income Taxes - MEC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current:
Federal	$ (1,650)	$ (1,463)	$ (1,701)
State	118	(65)	(177)
Total current	(1,442)	(1,449)	(1,778)
Deferred:
Federal	(114)	(408)	1,037
State	(275)	(49)	(476)
Total deferred	(356)	(462)	650
Investment tax credits	99	(5)	(4)
Total	(1,699)	(1,916)	(1,132)
MEC
Current:
Federal	(755)	(769)	(736)
State	(28)	(34)	(92)
Total current	(783)	(803)	(828)
Deferred:
Federal	109	77	189
State	(18)	(43)	(35)
Total deferred	91	34	154
Investment tax credits	(1)	(1)	(1)
Total	$ (693)	$ (770)	$ (675)