Statements of Changes in Shareholder's Equity (Unaudited) - MEC - USD ($) $ in Millions	Total	Additional Paid-in Capital	Retained Earnings	MEC	MEC Common Stock	MEC Additional Paid-in Capital	MEC Retained Earnings
Balance at Dec. 31, 2019				$ 7,240	$ 0	$ 561	$ 6,679
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 1,786			360			360
Other equity transactions	(1)	$ (1)
Balance at Jun. 30, 2020				7,600	0	561	7,039
Balance at Mar. 31, 2020				7,391	0	561	6,830
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,116			209			209
Balance at Jun. 30, 2020				7,600	0	561	7,039
Balance at Dec. 31, 2020	43,010			8,065	0	561	7,504
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,285			360			360
Other equity transactions	(1)			1			1
Balance at Jun. 30, 2021	45,412			8,426	0	561	7,865
Balance at Mar. 31, 2021				8,212	0	561	7,651
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,281			213			213
Other equity transactions	(4)		$ (1)	1			1
Balance at Jun. 30, 2021	$ 45,412			$ 8,426	$ 0	$ 561	$ 7,865