Income Taxes - MEC - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ (1,701)	$ (1,537)	$ (956)
State	(177)	(121)	(13)
Total current	(1,778)	(1,572)	(888)
Deferred:
Federal	1,037	1,438	431
State	(476)	424	(127)
Total deferred	650	1,883	296
Investment tax credits	(4)	(3)	(6)
Total	(1,132)	308	(598)
MEC
Current:
Federal	(736)	(684)	(478)
State	(92)	(94)	(47)
Total current	(828)	(778)	(525)
Deferred:
Federal	189	201	166
State	(35)	8	(11)
Total deferred	154	209	155
Investment tax credits	(1)	(1)	(1)
Total	$ (675)	$ (570)	$ (371)