Statements of Changes in Shareholder's Equity (Unaudited) - MEC - USD ($) $ in Millions	Total	Retained Earnings	MEC	MEC Common Stock	MEC Additional Paid-in Capital	MEC Retained Earnings
Balance at Dec. 31, 2022			$ 9,645	$ 0	$ 561	$ 9,084
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 989		242			242
Common stock dividend			(100)			(100)
Other equity transactions			1			1
Balance at Mar. 31, 2023			9,788	0	561	9,227
Balance at Dec. 31, 2023	48,434		9,603	0	561	9,042
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	653		238			238
Common stock dividend			(425)			(425)
Other equity transactions	(3)	$ (1)	(1)			(1)
Balance at Mar. 31, 2024	$ 48,959		$ 9,415	$ 0	$ 561	$ 8,854