Statements of Changes in Shareholder's Equity (Unaudited) - MEC - USD ($) $ in Millions	Total	MEC	MEC Common Stock	MEC Additional Paid-in Capital	MEC Retained Earnings
Balance at Dec. 31, 2020		$ 8,065	$ 0	$ 561	$ 7,504
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 4	147			147
Balance at Mar. 31, 2021		8,212	0	561	7,651
Balance at Dec. 31, 2021	46,694	8,960	0	561	8,399
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(129)	244			244
Balance at Mar. 31, 2022	$ 46,530	$ 9,204	$ 0	$ 561	$ 8,643